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sooks
QUOTE (Guest_Jim+Dec 2 2005, 10:43 PM)
Back to the Airplane for a minute . . .

if the conveyor belt created sufficient headwind for the aircraft (on account of the friction between the conveyor belt and the air) then the aircraft could actually take off faster than otherwise (Assuming frictionless wheels and an aircraft mounted engine).

theoretically i spose it would work..but the belt would have to be movingly ungodly fast as i dont think it produces that much wind.
Sage
QUOTE (sooks+Dec 2 2005, 11:57 PM)
QUOTE (Sage+Dec 2 2005, 11:13 PM)
QUOTE (Insyght+Dec 2 2005, 10:34 PM)
Grammer again?

If you put your car on a dyno and rev it till the speedo says 100mph, what speed would you say your car is traveling?

Looks like you are saying 0mph, because the car is on the dyno...

Look at the problem with you definition of "speed";

1. Car at 0 meters per sec (mps) wheel speed. Belt @ 0 mps. 0 mps movement physically forward.

2. Car at 10 mps wheel speed. Car will try and move forward physically 10mps. Belt must spin backwards @ car Speed (the physically moving forward speed). This results in all of the cars 10mps forward movement being sucked up in 10mps backwards speed of the belt, leaving as a result 10mps wheel speed, 10mps backwards belt speed and 0mps physical speed.

3. Car at 50  mps wheel speed. Car try to move forward 50mps, cant, cos belt must match forward speed, so you end up with wheel speed 50 mps, belt speed back 50 mps and physically moving forward speed 0mps.

Tell me. As what speed would have to travel for this logic to break and forward movement starting to occur?

You mean semantics not grammar but that's another debate.

I agree with all the examples you illustrate. But none of these describe the puzzle.

It's not my definition of speed. Find a textbook, Speed = Distance/Time. With no distance travelled the car has no speed no matter how fast you make the wheels rotate. With no distance travelled the car has not moved. The puzzle tells us the car (sorry, plane) moves.

Hold your hands out in front of you and point with each forefinger. Now put the tip of each forefinger on the table so that they are right next to each other. Move your right finger 6 inches to the right whilst simultaneously moving your left finger 6 inches to the left. They are now 12 inches apart, each finger having moved 6 inches over the same period of time. This exactly describes the motion of our plane/car and the belt in this puzzle. They each move (ie travel a fixed distance)at the same rate in opposite directions at the same time. How much thrust you need to apply, how fast you have to rev the engine, how quickly the wheels need to spin, is irrelevant the solving the puzzle.

what your explaining works for the plane..but does not work for the car. the car does not move... it will stay in place no matter how much you rev the engine. a perfect example is the moving walkways at an airport. if you walked on them backwards you have to wlak as fast as teh walkway to stay in the same place. if you walk slower than the belt youll move backwards...if you walk faster than the walkway youll move forward but at your walking speed - the walkway speed.

Sooks

It works just the same - I used this example already, read back a couple of pages.

You are confusing the speed your legs will have to walk with the speed at which you travel (ie the speed with which you move forward). The belt matches your movement not the speed you walk.
sooks
QUOTE (Sage+Dec 3 2005, 12:33 AM)
QUOTE (sooks+Dec 2 2005, 11:57 PM)
QUOTE (Sage+Dec 2 2005, 11:13 PM)
QUOTE (Insyght+Dec 2 2005, 10:34 PM)
Grammer again?

If you put your car on a dyno and rev it till the speedo says 100mph, what speed would you say your car is traveling?

Looks like you are saying 0mph, because the car is on the dyno...

Look at the problem with you definition of "speed";

1. Car at 0 meters per sec (mps) wheel speed. Belt @ 0 mps. 0 mps movement physically forward.

2. Car at 10 mps wheel speed. Car will try and move forward physically 10mps. Belt must spin backwards @ car Speed (the physically moving forward speed). This results in all of the cars 10mps forward movement being sucked up in 10mps backwards speed of the belt, leaving as a result 10mps wheel speed, 10mps backwards belt speed and 0mps physical speed.

3. Car at 50  mps wheel speed. Car try to move forward 50mps, cant, cos belt must match forward speed, so you end up with wheel speed 50 mps, belt speed back 50 mps and physically moving forward speed 0mps.

Tell me. As what speed would have to travel for this logic to break and forward movement starting to occur?

You mean semantics not grammar but that's another debate.

I agree with all the examples you illustrate. But none of these describe the puzzle.

It's not my definition of speed. Find a textbook, Speed = Distance/Time. With no distance travelled the car has no speed no matter how fast you make the wheels rotate. With no distance travelled the car has not moved. The puzzle tells us the car (sorry, plane) moves.

Hold your hands out in front of you and point with each forefinger. Now put the tip of each forefinger on the table so that they are right next to each other. Move your right finger 6 inches to the right whilst simultaneously moving your left finger 6 inches to the left. They are now 12 inches apart, each finger having moved 6 inches over the same period of time. This exactly describes the motion of our plane/car and the belt in this puzzle. They each move (ie travel a fixed distance)at the same rate in opposite directions at the same time. How much thrust you need to apply, how fast you have to rev the engine, how quickly the wheels need to spin, is irrelevant the solving the puzzle.

what your explaining works for the plane..but does not work for the car. the car does not move... it will stay in place no matter how much you rev the engine. a perfect example is the moving walkways at an airport. if you walked on them backwards you have to wlak as fast as teh walkway to stay in the same place. if you walk slower than the belt youll move backwards...if you walk faster than the walkway youll move forward but at your walking speed - the walkway speed.

Sooks

It works just the same - I used this example already, read back a couple of pages.

You are confusing the speed your legs will have to walk with the speed at which you travel (ie the speed with which you move forward). The belt matches your movement not the speed you walk.

But with no wheel slip, the speed of the car is the same as the speed of the wheels
PEK.
QUOTE (Guest+Dec 2 2005, 09:03 PM)

In fact it proves nothing whatsoever, because it doesn't even consider the power to weight ratio between the fan and the skateboard! The board itself is incredibly light compared to how much a jumbo would weigh. And the fan is out of proportion to the board and producing no thrust whatsoever.

What you're forgetting is the effect of gravity holding the plane down on the conveyor. Gravity needs to be overcome if the plane is going to fly.

So the fan produces no thrust? The board still manage to go forward.Then imagine what will happen when there is thrust like that from the engine from a plane.

According to your statement it sounds as if gravity only applies when the plane is on the belt, so if the plane was on the ground gravity will play no roll?

Rick
The plane intends to take off and would not be on that demonic runway unless the pilot thought it was possible. Aircraft manufacturers have been designing planes for special applications longer than conveyor belt runway manufacturers have been trying to frustrate aircraft departures.

In this case the aircraft manufacturer has designed its wheels (the problem does not limit inovative wheel design) to allow operations from demonic runways. The wheels are made of a super slick teflon plastic and are of narrow cross section. They are fitted with a spin retarding device that will allow them to turn just fast enough to prevent wearing flat spots on them as they simultaniously roll and skid on the conveyor belt surface during take off. The problem criteria says the wheels turn so this wheel design satisfies that condition by allowing the wheels to turn, but just not too fast. Of course the belt will match the speed of the turning wheels, but the plane will now be able to accelerate and take off.

The FAA and Transport Canada would not certify a plane unless it could take off and fly so the very fact that the plane "intends to take off" precludes that it will be able to do so if it is designed for the takeoff conditions it will face. The aircraft operating manual that must be on the plane wll include proceedures for various take off conditions such as, short field, soft field, high density altitude, cross wind, and demonic runways. If the pilot of this plane follows the demonic runway take off proceedure he will indeed fly. Why else would he be there trying?
guest 27
I hope to heck this was answered correctly and actually at a consensous between page 14 where I stopped reading and here - if not...

Yes, the plane will take off, if the direction of motion of the plane is in the forward direction and the force making the plane move is sufficient to attain take off speed.

Reason:

In the problem you have several constraints stated that must all be satisfied by the answer.

-The plane moves in one direction
-The conveyer moves in the opposite direction
-The plane and conveyer have measurable speed
-The speed of the conveyer and plane are equal

In order to satisfy all constraints of the problem the plane has to move relative to ground, the conveyer will also be moving relative to ground and both will have measurable speed relative to ground, although in opposite directions. (Ground being a fixed non-moving point separate from both the plane and the conveyer).

With this being true then the plane will be moving forward through the air, once it reaches the airspeed needed for takeoff, it will take off, regardless of the speed of the conveyer. In this case the only thing the conveyer does is make the wheels turn twice as fast as they normally would.

For the plane to not take off, it would have to be motionless, i.e. zero airspeed or speed relative to the ground. If that was true then the conveyer would have motion and speed relative to the ground, but the plane would not, and that violates the constraints of the problem as both have speed and motion..

Same thing from a point relative to the conveyer – the plane would have speed and motion to a person on the conveyer, but to the person on the conveyer, the conveyer would have neither speed nor motion, again violating the constraints of the problem.
Bloy
QUOTE (Insyght+Dec 2 2005, 09:03 PM)
The plane has been solved long ago... then someone included a CAR with wings (LOL) Which is different because of no-air thrust, so movement forward would not be possible...

Yet some feel as though the car would move forward, even though the riddle explicitly states that the belt matches car speed.

Look the riddle cannot be used on a CAR with wings?

Why? these two are mutually exclusive:

-> Belt matches speed of car
-> car moves forward.

Both are not possible with the car. Only one is.

If you say belt matches speed, then car cannot move.
If you say car moves, then belt cannot match speed.

Insyght..
of course the car will move forward.... otherwise there is no SPEED of the car.

..that is unless you refuse to notate the actual movement of the car and continue to rely on the illusion that the speed of the car is actually what the speedometer is reporting.
Under any conditions where the road(runway) surface moves the car's speedometer is unreliable when indicating the actual speed of the car.
Try using a radar gun to ascertain the actual speed of the car instead of insisting on what the car's speedometer says.

I only talk of a car with wings because so many prior posts were using examples of semis, treadmills, etc.
The only difference is that the wheel driven winged car will only reach the liftoff and go no faster. don't even look at what your speedometer reports..it isn't giving the true speed of the car.

You're right, the car will not fly, but you are also wrong because the car WILL move.

....some more frivolity
sooks
QUOTE (Bloy+Dec 3 2005, 03:36 PM)
QUOTE (Insyght+Dec 2 2005, 09:03 PM)
The plane has been solved long ago... then someone included a CAR with wings (LOL) Which is different because of no-air thrust, so movement forward would not be possible...

Yet some feel as though the car would move forward, even though the riddle explicitly states that the belt matches car speed.

Look the riddle cannot be used on a CAR with wings?

Why? these two are mutually exclusive:

-> Belt matches speed of car
-> car moves forward.

Both are not possible with the car. Only one is.

If you say belt matches speed, then car cannot move.
If you say car moves, then belt cannot match speed.

Insyght..
of course the car will move forward.... otherwise there is no SPEED of the car.

..that is unless you refuse to notate the actual movement of the car and continue to rely on the illusion that the speed of the car is actually what the speedometer is reporting.
Under any conditions where the road(runway) surface moves the car's speedometer is unreliable when indicating the actual speed of the car.
Try using a radar gun to ascertain the actual speed of the car instead of insisting on what the car's speedometer says.

I only talk of a car with wings because so many prior posts were using examples of semis, treadmills, etc.
The only difference is that the wheel driven winged car will only reach the liftoff and go no faster. don't even look at what your speedometer reports..it isn't giving the true speed of the car.

You're right, the car will not fly, but you are also wrong because the car WILL move.

....some more frivolity

Bloy,

I hate to keep bringing up this point..... but speed is all relative... yes there is speed of the car.... but its speed is relative to the belt. Your just getting mixed up in the semantics of the problem and trying to discern car speed and wheel speed. when in this case reality there is no difference unless there is wheel slip (which is unlike the plane because the wheels are moved by the engine). which there is none in this case relative to the belt. I hate to use the moving walkway again.. .. but if you ride a bicycle against the flow of the walkway at the same speed you are going nowhere. much like the one person who was using the boat example going upstream.... if the stream is flowing 10 mph and the boat is moving 10 mph.. then the boat is stationary. or even a plane once its in the air is flying at an airspeed of 80 mph into a 80 mph headwind, its speed relative to the ground is 0. I think your getting to deep into it and just try taking a step back and look at it like that and it should become clear.
Sage
QUOTE (sooks+Dec 3 2005, 05:36 PM)
QUOTE (Bloy+Dec 3 2005, 03:36 PM)
QUOTE (Insyght+Dec 2 2005, 09:03 PM)
The plane has been solved long ago... then someone included a CAR with wings (LOL) Which is different because of no-air thrust, so movement forward would not be possible...

Yet some feel as though the car would move forward, even though the riddle explicitly states that the belt matches car speed.

Look the riddle cannot be used on a CAR with wings?

Why? these two are mutually exclusive:

-> Belt matches speed of car
-> car moves forward.

Both are not possible with the car. Only one is.

If you say belt matches speed, then car cannot move.
If you say car moves, then belt cannot match speed.

Insyght..
of course the car will move forward.... otherwise there is no SPEED of the car.

..that is unless you refuse to notate the actual movement of the car and continue to rely on the illusion that the speed of the car is actually what the speedometer is reporting.
Under any conditions where the road(runway) surface moves the car's speedometer is unreliable when indicating the actual speed of the car.
Try using a radar gun to ascertain the actual speed of the car instead of insisting on what the car's speedometer says.

I only talk of a car with wings because so many prior posts were using examples of semis, treadmills, etc.
The only difference is that the wheel driven winged car will only reach the liftoff and go no faster. don't even look at what your speedometer reports..it isn't giving the true speed of the car.

You're right, the car will not fly, but you are also wrong because the car WILL move.

....some more frivolity

Bloy,

I hate to keep bringing up this point..... but speed is all relative... yes there is speed of the car.... but its speed is relative to the belt. Your just getting mixed up in the semantics of the problem and trying to discern car speed and wheel speed. when in this case reality there is no difference unless there is wheel slip (which is unlike the plane because the wheels are moved by the engine). which there is none in this case relative to the belt. I hate to use the moving walkway again.. .. but if you ride a bicycle against the flow of the walkway at the same speed you are going nowhere. much like the one person who was using the boat example going upstream.... if the stream is flowing 10 mph and the boat is moving 10 mph.. then the boat is stationary. or even a plane once its in the air is flying at an airspeed of 80 mph into a 80 mph headwind, its speed relative to the ground is 0. I think your getting to deep into it and just try taking a step back and look at it like that and it should become clear.

One last time!

Conveyor belt travels from A to B (lets say 1 mile) at 4 mph, so a point on the belt takes 15mins to travel from A to B. You are in a MINI at point B and wish to drive to point A, also in 15mins. To achieve this you need to drive the MINI at 8mph along the belt in order to overcome the movement of the belt. This is your speed relative to the belt. But you still cover the same distance in the same time so your true (actual) speed is the same as the belt, ie 4mph.

Your problem is that you are comparing the relative speed of the car/belt with the actual speed of the belt. You must compare apple with apples. Actual speed of car and belt is 4mph because they each cover the actual 1 mile in 15mins. From sitting in the car you view your speed relative to the belt as 8mph. If you were sat on the belt your relative speed to the car is still 8mph.

Either way the relative (car-belt) speed is equal, the actual speed (car-belt) is equal. These are the conditions of the puzzle. The car moves, the car flies.
sooks
QUOTE (Sage+Dec 3 2005, 07:47 PM)
QUOTE (sooks+Dec 3 2005, 05:36 PM)
QUOTE (Bloy+Dec 3 2005, 03:36 PM)
QUOTE (Insyght+Dec 2 2005, 09:03 PM)
The plane has been solved long ago... then someone included a CAR with wings (LOL) Which is different because of no-air thrust, so movement forward would not be possible...

Yet some feel as though the car would move forward, even though the riddle explicitly states that the belt matches car speed.

Look the riddle cannot be used on a CAR with wings?

Why? these two are mutually exclusive:

-> Belt matches speed of car
-> car moves forward.

Both are not possible with the car. Only one is.

If you say belt matches speed, then car cannot move.
If you say car moves, then belt cannot match speed.

Insyght..
of course the car will move forward.... otherwise there is no SPEED of the car.

..that is unless you refuse to notate the actual movement of the car and continue to rely on the illusion that the speed of the car is actually what the speedometer is reporting.
Under any conditions where the road(runway) surface moves the car's speedometer is unreliable when indicating the actual speed of the car.
Try using a radar gun to ascertain the actual speed of the car instead of insisting on what the car's speedometer says.

I only talk of a car with wings because so many prior posts were using examples of semis, treadmills, etc.
The only difference is that the wheel driven winged car will only reach the liftoff and go no faster. don't even look at what your speedometer reports..it isn't giving the true speed of the car.

You're right, the car will not fly, but you are also wrong because the car WILL move.

....some more frivolity

Bloy,

I hate to keep bringing up this point..... but speed is all relative... yes there is speed of the car.... but its speed is relative to the belt. Your just getting mixed up in the semantics of the problem and trying to discern car speed and wheel speed. when in this case reality there is no difference unless there is wheel slip (which is unlike the plane because the wheels are moved by the engine). which there is none in this case relative to the belt. I hate to use the moving walkway again.. .. but if you ride a bicycle against the flow of the walkway at the same speed you are going nowhere. much like the one person who was using the boat example going upstream.... if the stream is flowing 10 mph and the boat is moving 10 mph.. then the boat is stationary. or even a plane once its in the air is flying at an airspeed of 80 mph into a 80 mph headwind, its speed relative to the ground is 0. I think your getting to deep into it and just try taking a step back and look at it like that and it should become clear.

One last time!

Conveyor belt travels from A to B (lets say 1 mile) at 4 mph, so a point on the belt takes 15mins to travel from A to B. You are in a MINI at point B and wish to drive to point A, also in 15mins. To achieve this you need to drive the MINI at 8mph along the belt in order to overcome the movement of the belt. This is your speed relative to the belt. But you still cover the same distance in the same time so your true (actual) speed is the same as the belt, ie 4mph.

Your problem is that you are comparing the relative speed of the car/belt with the actual speed of the belt. You must compare apple with apples. Actual speed of car and belt is 4mph because they each cover the actual 1 mile in 15mins. From sitting in the car you view your speed relative to the belt as 8mph. If you were sat on the belt your relative speed to the car is still 8mph.

Either way the relative (car-belt) speed is equal, the actual speed (car-belt) is equal. These are the conditions of the puzzle. The car moves, the car flies.

What you just said made absolutely no sense.... you completely agreed with what i was saying in the first part in the fact that car has to move twice as fast as the belt to be moving..... and your saying that the speed is relevant. but the car isnt going twice as fast as the belt...the belt and the car are going at the same speed..thus stationary...

ok ok....i just reread your quote... i get what your saying... your saying that the belt is matching the speed of car relative to the earth. So essentially what your saying makes sense... but still untrue. Thats where it comes back to the semantics of the problem... and it being somewhat poorly worded. It doesnt really make sense that the belt would be matching the speed relative to the ground. its not really even feasible. it would have to be measuring the cars speed relative to itself and then subtract its own speed and simultaneously change its speed.....but thats circular logic...it just doesnt work....
sooks
QUOTE (Sage+Dec 3 2005, 07:47 PM)
QUOTE (sooks+Dec 3 2005, 05:36 PM)
QUOTE (Bloy+Dec 3 2005, 03:36 PM)
QUOTE (Insyght+Dec 2 2005, 09:03 PM)
The plane has been solved long ago... then someone included a CAR with wings (LOL) Which is different because of no-air thrust, so movement forward would not be possible...

Yet some feel as though the car would move forward, even though the riddle explicitly states that the belt matches car speed.

Look the riddle cannot be used on a CAR with wings?

Why? these two are mutually exclusive:

-> Belt matches speed of car
-> car moves forward.

Both are not possible with the car. Only one is.

If you say belt matches speed, then car cannot move.
If you say car moves, then belt cannot match speed.

Insyght..
of course the car will move forward.... otherwise there is no SPEED of the car.

..that is unless you refuse to notate the actual movement of the car and continue to rely on the illusion that the speed of the car is actually what the speedometer is reporting.
Under any conditions where the road(runway) surface moves the car's speedometer is unreliable when indicating the actual speed of the car.
Try using a radar gun to ascertain the actual speed of the car instead of insisting on what the car's speedometer says.

I only talk of a car with wings because so many prior posts were using examples of semis, treadmills, etc.
The only difference is that the wheel driven winged car will only reach the liftoff and go no faster. don't even look at what your speedometer reports..it isn't giving the true speed of the car.

You're right, the car will not fly, but you are also wrong because the car WILL move.

....some more frivolity

Bloy,

I hate to keep bringing up this point..... but speed is all relative... yes there is speed of the car.... but its speed is relative to the belt. Your just getting mixed up in the semantics of the problem and trying to discern car speed and wheel speed. when in this case reality there is no difference unless there is wheel slip (which is unlike the plane because the wheels are moved by the engine). which there is none in this case relative to the belt. I hate to use the moving walkway again.. .. but if you ride a bicycle against the flow of the walkway at the same speed you are going nowhere. much like the one person who was using the boat example going upstream.... if the stream is flowing 10 mph and the boat is moving 10 mph.. then the boat is stationary. or even a plane once its in the air is flying at an airspeed of 80 mph into a 80 mph headwind, its speed relative to the ground is 0. I think your getting to deep into it and just try taking a step back and look at it like that and it should become clear.

One last time!

Conveyor belt travels from A to B (lets say 1 mile) at 4 mph, so a point on the belt takes 15mins to travel from A to B. You are in a MINI at point B and wish to drive to point A, also in 15mins. To achieve this you need to drive the MINI at 8mph along the belt in order to overcome the movement of the belt. This is your speed relative to the belt. But you still cover the same distance in the same time so your true (actual) speed is the same as the belt, ie 4mph.

Your problem is that you are comparing the relative speed of the car/belt with the actual speed of the belt. You must compare apple with apples. Actual speed of car and belt is 4mph because they each cover the actual 1 mile in 15mins. From sitting in the car you view your speed relative to the belt as 8mph. If you were sat on the belt your relative speed to the car is still 8mph.

Either way the relative (car-belt) speed is equal, the actual speed (car-belt) is equal. These are the conditions of the puzzle. The car moves, the car flies.

also, you cnat really compare the car and plane in that scenario...cause they are two completly opposite things if your tlaking about the belt matching the cars speed realtive to the gound...those just arent the same
sooks
QUOTE (sooks+Dec 3 2005, 08:50 PM)
QUOTE (Sage+Dec 3 2005, 07:47 PM)
QUOTE (sooks+Dec 3 2005, 05:36 PM)
QUOTE (Bloy+Dec 3 2005, 03:36 PM)
QUOTE (Insyght+Dec 2 2005, 09:03 PM)
The plane has been solved long ago... then someone included a CAR with wings (LOL) Which is different because of no-air thrust, so movement forward would not be possible...

Yet some feel as though the car would move forward, even though the riddle explicitly states that the belt matches car speed.

Look the riddle cannot be used on a CAR with wings?

Why? these two are mutually exclusive:

-> Belt matches speed of car
-> car moves forward.

Both are not possible with the car. Only one is.

If you say belt matches speed, then car cannot move.
If you say car moves, then belt cannot match speed.

Insyght..
of course the car will move forward.... otherwise there is no SPEED of the car.

..that is unless you refuse to notate the actual movement of the car and continue to rely on the illusion that the speed of the car is actually what the speedometer is reporting.
Under any conditions where the road(runway) surface moves the car's speedometer is unreliable when indicating the actual speed of the car.
Try using a radar gun to ascertain the actual speed of the car instead of insisting on what the car's speedometer says.

I only talk of a car with wings because so many prior posts were using examples of semis, treadmills, etc.
The only difference is that the wheel driven winged car will only reach the liftoff and go no faster. don't even look at what your speedometer reports..it isn't giving the true speed of the car.

You're right, the car will not fly, but you are also wrong because the car WILL move.

....some more frivolity

Bloy,

I hate to keep bringing up this point..... but speed is all relative... yes there is speed of the car.... but its speed is relative to the belt. Your just getting mixed up in the semantics of the problem and trying to discern car speed and wheel speed. when in this case reality there is no difference unless there is wheel slip (which is unlike the plane because the wheels are moved by the engine). which there is none in this case relative to the belt. I hate to use the moving walkway again.. .. but if you ride a bicycle against the flow of the walkway at the same speed you are going nowhere. much like the one person who was using the boat example going upstream.... if the stream is flowing 10 mph and the boat is moving 10 mph.. then the boat is stationary. or even a plane once its in the air is flying at an airspeed of 80 mph into a 80 mph headwind, its speed relative to the ground is 0. I think your getting to deep into it and just try taking a step back and look at it like that and it should become clear.

One last time!

Conveyor belt travels from A to B (lets say 1 mile) at 4 mph, so a point on the belt takes 15mins to travel from A to B. You are in a MINI at point B and wish to drive to point A, also in 15mins. To achieve this you need to drive the MINI at 8mph along the belt in order to overcome the movement of the belt. This is your speed relative to the belt. But you still cover the same distance in the same time so your true (actual) speed is the same as the belt, ie 4mph.

Your problem is that you are comparing the relative speed of the car/belt with the actual speed of the belt. You must compare apple with apples. Actual speed of car and belt is 4mph because they each cover the actual 1 mile in 15mins. From sitting in the car you view your speed relative to the belt as 8mph. If you were sat on the belt your relative speed to the car is still 8mph.

Either way the relative (car-belt) speed is equal, the actual speed (car-belt) is equal. These are the conditions of the puzzle. The car moves, the car flies.

What you just said made absolutely no sense.... you completely agreed with what i was saying in the first part in the fact that car has to move twice as fast as the belt to be moving..... and your saying that the speed is relevant. but the car isnt going twice as fast as the belt...the belt and the car are going at the same speed..thus stationary...

ok ok....i just reread your quote... i get what your saying... your saying that the belt is matching the speed of car relative to the earth. So essentially what your saying makes sense... but still untrue. Thats where it comes back to the semantics of the problem... and it being somewhat poorly worded. It doesnt really make sense that the belt would be matching the speed relative to the ground. its not really even feasible. it would have to be measuring the cars speed relative to itself and then subtract its own speed and simultaneously change its speed.....but thats circular logic...it just doesnt work....

also, you cant be saying actual speed. speed doesnt state direction or position... there really is no such thing as actual speed...only speed compared to something else
Sage
Sooks

The plane moves - the puzzle says so. Remaining stationary with the wheels spinning on a moving belt does not constitute movement... I understand why/how you have reached your conclusion but you are overlooking this explicitly stated fact. If the plane moves, then my position is right. If the doesn't move then of course the plane cannot take off. But I can find no way of convincing myself that the plane doesn't move. I do not see how this part of this question can be up for debate as it is unambiguous. If you just take the part about matching speeds in isolation, then I can see the ambiguity. But as soon as you add the fact that the plane moves then there is only one right answer.

Put a GPS on the belt at A and a GPS in the car/plane at B. The car moves from B to A in 15mins, the belt moves from A to B in 15mins. At what speed does the GPS record both the car and belt? They will both have travelled at 4mph, exactly the same, just as the puzzle states. The fact that you, as the driver, had to make the car go at 8mph to achieve this is not relevant. You have still only covered that distance at a rate of 4mph, just like the belt. Remember you can only compare actual speed with actual or relative speed with relative speed, to mix the becomes a nonsense.

I really must bow out now as I can see no way for me to add to what I have already said over the last few pages. To everyone reading who still thinks the plane can't fly, I wish you all the best of luck. I'm sure that if you stick with it the dawn will eventually come.
sooks
QUOTE (Sage+Dec 3 2005, 10:05 PM)
Sooks

The plane moves - the puzzle says so. Remaining stationary with the wheels spinning on a moving belt does not constitute movement... I understand why/how you have reached your conclusion but you are overlooking this explicitly stated fact. If the plane moves, then my position is right. If the doesn't move then of course the plane cannot take off. But I can find no way of convincing myself that the plane doesn't move. I do not see how this part of this question can be up for debate as it is unambiguous. If you just take the part about matching speeds in isolation, then I can see the ambiguity. But as soon as you add the fact that the plane moves then there is only one right answer.

Put a GPS on the belt at A and a GPS in the car/plane at B. The car moves from B to A in 15mins, the belt moves from A to B in 15mins. At what speed does the GPS record both the car and belt? They will both have travelled at 4mph, exactly the same, just as the puzzle states. The fact that you, as the driver, had to make the car go at 8mph to achieve this is not relevant. You have still only covered that distance at a rate of 4mph, just like the belt. Remember you can only compare actual speed with actual or relative speed with relative speed, to mix the becomes a nonsense.

I really must bow out now as I can see no way for me to add to what I have already said over the last few pages. To everyone reading who still thinks the plane can't fly, I wish you all the best of luck. I'm sure that if you stick with it the dawn will eventually come.

Sage,

Ive always said the plane would move, i was one of the first advocates that said it would move........the plane will take off wiht the wheels spinning twice as fast as they normally would at take off speed. i was saying the car(wings or not) will not go anywhere....... there is one specific fact that differs the car and the plane. The fact of how the energy or movement is transfered. The thrust pushes the airplane, wheels are freespinning... cars engine turns drive train which turns wheel...wheels arent freespinning. thus for the plane it makes wheels belt negligible, for a car its not...depends on the ground to turn. I totally agree with all your examples your using...your exactly right on that fact, but with the car it wont go anywhere... its the only thing that makes sense. your math makes sense..... your just interpreting it wrong. the belt is only matching the speed of the car with relation to itself. it doesnt make sense to relate it to earth...that doesnt work.
Sage
QUOTE (sooks+Dec 3 2005, 10:38 PM)
there is one specific fact that differs the car and the plane. The fact of how the energy or movement is transfered. The thrust pushes the airplane, wheels are freespinning... cars engine turns drive train which turns wheel...wheels arent freespinning.

Yes, agreed but the puzzle states that the belt matches the movement of the plane, not the rotational speed of the wheels. It does not make one jot of difference how the motion is imparted - it works the same for a car or plane or person walking.

I am sure you don't mean to imply that it is impossible for a car to move forward against the motion of the belt? Have you never run up a down escalator - same thing, surely. Do you accept that a car can move forward against the flow of the belt? If so, then reread my last example. How can it be interpreted any other way?

BTW, although we disagree on the car thing, it is refreshing that you have kept your debate civil and constructive.

sooks
QUOTE (Sage+Dec 4 2005, 12:04 AM)
QUOTE (sooks+Dec 3 2005, 10:38 PM)
there is one specific fact that differs the car and the plane.  The fact of how the energy or movement is transfered.  The thrust pushes the airplane, wheels are freespinning...  cars engine turns drive train which turns wheel...wheels arent freespinning.

Yes, agreed but the puzzle states that the belt matches the movement of the plane, not the rotational speed of the wheels. It does not make one jot of difference how the motion is imparted - it works the same for a car or plane or person walking.

I am sure you don't mean to imply that it is impossible for a car to move forward against the motion of the belt? Have you never run up a down escalator - same thing, surely. Do you accept that a car can move forward against the flow of the belt? If so, then reread my last example. How can it be interpreted any other way?

BTW, although we disagree on the car thing, it is refreshing that you have kept your debate civil and constructive.

I almost think its silly were arguing this example. Cause its clear that we both understand how each works. Were basically just arguing the wording of the questionI do understand that the car can over come the speed of the belt. and yes it does not state that it matches the wheel speed. but it never states that it matches the ground speed either. Do you accept the fact that if the belt is matching the wheel speed then it isnt going anywhere? i was just stating that it isnt logical for the belt to match the ground speed. in theory i guess it works...but think about how it is possible to do that.... there is no way....for the belt to be reading it
sooks
QUOTE (Sage+Dec 4 2005, 12:04 AM)
QUOTE (sooks+Dec 3 2005, 10:38 PM)
there is one specific fact that differs the car and the plane.  The fact of how the energy or movement is transfered.  The thrust pushes the airplane, wheels are freespinning...  cars engine turns drive train which turns wheel...wheels arent freespinning.

Yes, agreed but the puzzle states that the belt matches the movement of the plane, not the rotational speed of the wheels. It does not make one jot of difference how the motion is imparted - it works the same for a car or plane or person walking.

I am sure you don't mean to imply that it is impossible for a car to move forward against the motion of the belt? Have you never run up a down escalator - same thing, surely. Do you accept that a car can move forward against the flow of the belt? If so, then reread my last example. How can it be interpreted any other way?

BTW, although we disagree on the car thing, it is refreshing that you have kept your debate civil and constructive.

I agree with your statement about it being refreshing with a civil debate. you have made some very excellent points. and its entertaining to have an intelligent conversation over it without it getting heated.

*note: i meant to say debating not arguing in my previous post.
Guest
The problem is that the puzzle contradicts itself. It says that the plane moves, but it also says that the conveyor moves at exactly the same velocity in the opposite direction.

This prevents the plane from moving (or the car, or whatever is sitting on the conveyor at the time). It doesn't matter whether the thrust is coming from the jet, the propellor, the wheels, or two blokes standing on the conveyor and pushing it from behind!!! It really makes no difference!

The vehicle is acting against the resistance of the conveyor flowing in the opposite direction. If the vehicle's only applying the same amount of force forwards, it will never actually gain any forwards velocity in relation to the ground. At best it will only remain stationary on the conveyor. This is basic Newtonian physics. Two equal forces acting on the same object in opposite directions cancel each other out.

If this is not the case, then if the conveyor is moving backwards, how much thrust does the vehicle have to apply in order to remain stationary in relation to the ground? Exactly the same amount as the conveyor is applying, but in the opposite direction! It doesn't matter whether the thrust is being applied by the jet or by the wheels.

If you start the conveyor off going backwards on it's own, then the plane starts moving backwards with it. It has to apply the same amount of force forwards in order to stop itself from moving backwards in relation to the ground. Any more force than this that it applies, registers on the conveyors sensors as forwards velocity of the vehicle (up until that point it's only been registering negative or zero velocity), and according to the puzzle the conveyor would then increase it's own speed backwards to match the forwards velocity.

So say that the conveyor was moving backwards at 5mph, and the vehicle was applying that same amount of force to go forwards. The plane is now 'stationary'. If the plane now tries to apply any more force to make it go at 6mph (and hence 1mph in actual forwards velocity), the conveyor senses this change and applies the same amount backwards and you're back where you started. Both forces acting equally on the same object.

The vehicle would never be able to move forwards!! The conveyor would always match whatever the vehicle did, no matter what speed it was attempting to push forwards at.

sooks
QUOTE (Guest+Dec 4 2005, 12:25 AM)
The problem is that the puzzle contradicts itself. It says that the plane moves, but it also says that the conveyor moves at exactly the same velocity in the opposite direction.

This prevents the plane from moving (or the car, or whatever is sitting on the conveyor at the time). It doesn't matter whether the thrust is coming from the jet, the propellor, the wheels, or two blokes standing on the conveyor and pushing it from behind!!! It really makes no difference!

The vehicle is acting against the resistance of the conveyor flowing in the opposite direction. If the vehicle's only applying the same amount of force forwards, it will never actually gain any forwards velocity in relation to the ground. At best it will only remain stationary on the conveyor. This is basic Newtonian physics. Two equal forces acting on the same object in opposite directions cancel each other out.

If this is not the case, then if the conveyor is moving backwards, how much thrust does the vehicle have to apply in order to remain stationary in relation to the ground? Exactly the same amount as the conveyor is applying, but in the opposite direction! It doesn't matter whether the thrust is being applied by the jet or by the wheels.

If you start the conveyor off going backwards on it's own, then the plane starts moving backwards with it. It has to apply the same amount of force forwards in order to stop itself from moving backwards in relation to the ground. Any more force than this that it applies, registers on the conveyors sensors as forwards velocity of the vehicle (up until that point it's only been registering negative or zero velocity), and according to the puzzle the conveyor would then increase it's own speed backwards to match the forwards velocity.

So say that the conveyor was moving backwards at 5mph, and the vehicle was applying that same amount of force to go forwards. The plane is now 'stationary'. If the plane now tries to apply any more force to make it go at 6mph (and hence 1mph in actual forwards velocity), the conveyor senses this change and applies the same amount backwards and you're back where you started. Both forces acting equally on the same object.

The vehicle would never be able to move forwards!! The conveyor would always match whatever the vehicle did, no matter what speed it was attempting to push forwards at.

Despite the fact that we have covered this several times and it had been resolved ill sum it up. Your right about what your saying about the car. the car must move at the same speed in the opposite direction of the belt. the plane is different...it doesnt require the wheels to move. the wheels and belt are negligble. pretty muvch no matter how fast the belt is moving, the plane will take off. the only force resisting it would be the force withing the wheel bearings. which compared to the thurst of the engine is extremly minute. essentially the plane will take off with the wheels going twice as fast as they normally would at takeoff. do a free body diagram on it and youllsee how it works.

another way to think of it is.... put a plane on ice....witth skis instead of wheels...itll still move.....or even if you put cinder blocks instead of wheels on pavement...it will still move....not nearly as well cause there is much more friction. the wheels are just a platform for the plane and to cause less resistance.
useful idiot
OK, let's figure out why the airplane will fly.

Manfred's in the airplane. Old Hack has the Army-surplus crane fired up and he's picking up the J-3 and Manfred and carrying them over to Runway 27, which has been transformed into a 3,000-foot conveyor belt. It is a calm day. The conveyor drive is programmed so that if Manfred can start to move in the J-3, if he can generate any airspeed or groundspeed, the conveyor will move toward the east (remember Manfred and the J-3 are facing west) at exactly the speed of the air/groundspeed. Because the wind is calm, if Manfred can generate any indicated airspeed, he will also be generating precisely the same groundspeed. Groundspeed, of course being relative to the ground of the airport surrounding the conveyor belt runway. So, the speed of the conveyor belt eastbound will be the same as Manfred's indicated airspeed, westbound.

Manfred does his prestart checklist, holds the heel brakes, hits the starter and the little Continental up front clatters to life. Oil pressure comes up and stabilizes and Manfred tries to look busy because the eyes of the world are upon him, but all he can do is make sure the fuel is on and the altimeter and trim are set, then do a quick runup to check the mags and the carb heat. He moves the controls through their full travel and glares at the ailerons, doing his best to look heroic, then holds the stick aft in the slipstream to pin the tail and lets go of the brakes.

Baron of the Belt

So far the J-3 has not moved, nor has the conveyor. At idle power, there's not enough thrust to move the J-3 forward on a level surface, so Manfred starts to bring up the power, intending to take off. The propeller rpm increases and the prop shoves air aft, as it does on every takeoff, causing the airplane to move forward through the air, and as a consequence, forward with regard to the ground. Simultaneously the conveyor creaks to life, moving east, under the tires of the J-3. As the J-3 thrusts its way through the air, driven by its propeller, the airspeed indicator comes off the peg at about 10 mph. At that moment the conveyor is moving at 10 mph to the east and the tires are whirling around at 20 mph because the prop has pulled it to an airspeed, and groundspeed, of 10 mph, westbound. The airplane is moving relative to the still air and the ground at 10 mph, but with regard to the conveyor, which is going the other way at 10 mph, the relative speed is 20 mph.

Manfred relaxes a bit because the conveyor cannot stop him from moving forward. There is nothing on the airplane that pushes against the ground or the conveyor in order for it to accelerate; as Karen -- one of our techies here at the Lounge -- put it, the airplane freewheels. In technical terms, there is some bearing drag on the wheels, but it's under 40 pounds, and the engine has overcome that for years; plus the drag doesn't increase significantly as the wheel speed increases. Unless Manfred applies the brakes, the conveyor cannot affect the rate at which the airplane accelerates.

A few moments later, the roaring Continental, spinning that wooden Sensenich prop, has accelerated the J-3 and Manfred to 25 mph indicated airspeed. He and the airplane are cruising past the cheering spectators at 25 mph, while the conveyor has accelerated to 25 mph eastbound, yet it still has no way of stopping the airplane's movement through the air. The wheels are spinning at 50 mph, so the noise level is a little high, but otherwise, the J-3 is making a normal, calm-wind takeoff.

As the indicated airspeed passes 45 mph, groundspeed -- you know, relative to where all those spectators are standing beside the conveyor belt -- is also 45 mph. (At least that's what it says on Manfred's GPS. Being brought back to life seemed to create an insatiable desire for electronic stuff.) The conveyor is also at 45 mph, and the wheels are whizzing around at 90 -- the groundspeed plus the speed of the conveyor in the opposite direction.

Manfred breaks ground, climbs a few hundred feet, then makes a low pass to see if he can terrify the spectators because they are Americans, descendants of those who defeated his countrymen back in 1918.

(Don't try this at home!)
(Don't try this at home!)

While the speed of the conveyor belt in the opposite direction is superficially attractive in saying the airplane cannot accelerate, it truly is irrelevant to what is happening with the airplane, because the medium on which it is acting is the air. The only time it could be a problem is if the wheel speed got so high that the tires blew out.

Put another way, consider the problem with the J-3 mounted on a hovercraft body (yes, similar things were tried about 30 years ago). The hovercraft lifts the airplane a fraction of an inch above the conveyor belt, and so no matter how fast the conveyor spins, it cannot prevent the propeller -- acting on the air -- from accelerating the airplane to takeoff speed. It's the same with wheels rolling on the conveyor belt. Those wheels are not powered and thus do not push against the belt to accelerate the airplane. Were that the case, the vehicle could not reach an airspeed needed to fly, because then the conveyor, the medium acted upon by the propulsive force, would be able to negate the acceleration relative to the air and ground.

I'm reminded of the New York Times editorial when Robert Goddard's rocket experiments were first being publicized. The author of the editorial said that rockets can't work in space because they have nothing to push against. It was laughably wrong, ignoring one of Sir Isaac's laws of physics that for every action there is an equal and opposite reaction. Here the propeller is pushing against the air, as it does every time an airplane takes off. How fast the airplane is moving over the surface on which its wheels rest is irrelevant; the medium is the magic. On a normal takeoff -- no conveyor involved -- if there is a 20 mph headwind, Manfred and the J-3 will lift off at 45 mph indicated airspeed; but relative to the ground, it is only 25 mph. Should the wind increase to 45 mph and if Manfred can get to the runway, he can take off without rolling an inch. His airspeed is 45 and groundspeed is zero. It is not necessary to have any groundspeed to fly, just airspeed. Conversely, if Manfred has a lot of runway and nothing to hit, and takes off downwind in a 25 mph tailwind, the propeller will have to accelerate the airplane to a zero airspeed, which will be a 25 mph groundspeed, and then on to a 45 mph airspeed, which will have him humming across the ground at 70 mph. The speed over the ground, or a conveyor belt, when an airplane takes off is irrelevant; all that matters is its speed through the air, and unless the pilot sets the brakes, a moving conveyor belt -- under the freely turning wheels -- cannot stop the process of acceleration.

Things eventually calmed down as the number of "it won't fly" folks dwindled as they began to understand that the airplane would take off. Old Hack looked at me and suggested we depart as the few holdouts showed no sign of changing their position. So, we headed out into the night to watch the guys take the conveyor out and reinstall the runway.

That was a cut and paste from http://avweb.com/news/columns/191034-1.html
sooks
QUOTE (useful idiot+Dec 4 2005, 01:54 AM)
OK, let's figure out why the airplane will fly.

Manfred's in the airplane. Old Hack has the Army-surplus crane fired up and he's picking up the J-3 and Manfred and carrying them over to Runway 27, which has been transformed into a 3,000-foot conveyor belt. It is a calm day. The conveyor drive is programmed so that if Manfred can start to move in the J-3, if he can generate any airspeed or groundspeed, the conveyor will move toward the east (remember Manfred and the J-3 are facing west) at exactly the speed of the air/groundspeed. Because the wind is calm, if Manfred can generate any indicated airspeed, he will also be generating precisely the same groundspeed. Groundspeed, of course being relative to the ground of the airport surrounding the conveyor belt runway. So, the speed of the conveyor belt eastbound will be the same as Manfred's indicated airspeed, westbound.

Manfred does his prestart checklist, holds the heel brakes, hits the starter and the little Continental up front clatters to life. Oil pressure comes up and stabilizes and Manfred tries to look busy because the eyes of the world are upon him, but all he can do is make sure the fuel is on and the altimeter and trim are set, then do a quick runup to check the mags and the carb heat. He moves the controls through their full travel and glares at the ailerons, doing his best to look heroic, then holds the stick aft in the slipstream to pin the tail and lets go of the brakes.

Baron of the Belt

So far the J-3 has not moved, nor has the conveyor. At idle power, there's not enough thrust to move the J-3 forward on a level surface, so Manfred starts to bring up the power, intending to take off. The propeller rpm increases and the prop shoves air aft, as it does on every takeoff, causing the airplane to move forward through the air, and as a consequence, forward with regard to the ground. Simultaneously the conveyor creaks to life, moving east, under the tires of the J-3. As the J-3 thrusts its way through the air, driven by its propeller, the airspeed indicator comes off the peg at about 10 mph. At that moment the conveyor is moving at 10 mph to the east and the tires are whirling around at 20 mph because the prop has pulled it to an airspeed, and groundspeed, of 10 mph, westbound. The airplane is moving relative to the still air and the ground at 10 mph, but with regard to the conveyor, which is going the other way at 10 mph, the relative speed is 20 mph.

Manfred relaxes a bit because the conveyor cannot stop him from moving forward. There is nothing on the airplane that pushes against the ground or the conveyor in order for it to accelerate; as Karen -- one of our techies here at the Lounge -- put it, the airplane freewheels. In technical terms, there is some bearing drag on the wheels, but it's under 40 pounds, and the engine has overcome that for years; plus the drag doesn't increase significantly as the wheel speed increases. Unless Manfred applies the brakes, the conveyor cannot affect the rate at which the airplane accelerates.

A few moments later, the roaring Continental, spinning that wooden Sensenich prop, has accelerated the J-3 and Manfred to 25 mph indicated airspeed. He and the airplane are cruising past the cheering spectators at 25 mph, while the conveyor has accelerated to 25 mph eastbound, yet it still has no way of stopping the airplane's movement through the air. The wheels are spinning at 50 mph, so the noise level is a little high, but otherwise, the J-3 is making a normal, calm-wind takeoff.

As the indicated airspeed passes 45 mph, groundspeed -- you know, relative to where all those spectators are standing beside the conveyor belt -- is also 45 mph. (At least that's what it says on Manfred's GPS. Being brought back to life seemed to create an insatiable desire for electronic stuff.) The conveyor is also at 45 mph, and the wheels are whizzing around at 90 -- the groundspeed plus the speed of the conveyor in the opposite direction.

Manfred breaks ground, climbs a few hundred feet, then makes a low pass to see if he can terrify the spectators because they are Americans, descendants of those who defeated his countrymen back in 1918.

(Don't try this at home!)
(Don't try this at home!)

While the speed of the conveyor belt in the opposite direction is superficially attractive in saying the airplane cannot accelerate, it truly is irrelevant to what is happening with the airplane, because the medium on which it is acting is the air. The only time it could be a problem is if the wheel speed got so high that the tires blew out.

Put another way, consider the problem with the J-3 mounted on a hovercraft body (yes, similar things were tried about 30 years ago). The hovercraft lifts the airplane a fraction of an inch above the conveyor belt, and so no matter how fast the conveyor spins, it cannot prevent the propeller -- acting on the air -- from accelerating the airplane to takeoff speed. It's the same with wheels rolling on the conveyor belt. Those wheels are not powered and thus do not push against the belt to accelerate the airplane. Were that the case, the vehicle could not reach an airspeed needed to fly, because then the conveyor, the medium acted upon by the propulsive force, would be able to negate the acceleration relative to the air and ground.

I'm reminded of the New York Times editorial when Robert Goddard's rocket experiments were first being publicized. The author of the editorial said that rockets can't work in space because they have nothing to push against. It was laughably wrong, ignoring one of Sir Isaac's laws of physics that for every action there is an equal and opposite reaction. Here the propeller is pushing against the air, as it does every time an airplane takes off. How fast the airplane is moving over the surface on which its wheels rest is irrelevant; the medium is the magic. On a normal takeoff -- no conveyor involved -- if there is a 20 mph headwind, Manfred and the J-3 will lift off at 45 mph indicated airspeed; but relative to the ground, it is only 25 mph. Should the wind increase to 45 mph and if Manfred can get to the runway, he can take off without rolling an inch. His airspeed is 45 and groundspeed is zero. It is not necessary to have any groundspeed to fly, just airspeed. Conversely, if Manfred has a lot of runway and nothing to hit, and takes off downwind in a 25 mph tailwind, the propeller will have to accelerate the airplane to a zero airspeed, which will be a 25 mph groundspeed, and then on to a 45 mph airspeed, which will have him humming across the ground at 70 mph. The speed over the ground, or a conveyor belt, when an airplane takes off is irrelevant; all that matters is its speed through the air, and unless the pilot sets the brakes, a moving conveyor belt -- under the freely turning wheels -- cannot stop the process of acceleration.

Things eventually calmed down as the number of "it won't fly" folks dwindled as they began to understand that the airplane would take off. Old Hack looked at me and suggested we depart as the few holdouts showed no sign of changing their position. So, we headed out into the night to watch the guys take the conveyor out and reinstall the runway.

That was a cut and paste from http://avweb.com/news/columns/191034-1.html

thank you for reposting the link i sent earlier..... by far is the best description
Sage
QUOTE (Guest+Dec 4 2005, 12:25 AM)
The problem is that the puzzle contradicts itself. It says that the plane moves, but it also says that the conveyor moves at exactly the same velocity in the opposite direction.

This prevents the plane from moving (or the car, or whatever is sitting on the conveyor at the time). It doesn't matter whether the thrust is coming from the jet, the propellor, the wheels, or two blokes standing on the conveyor and pushing it from behind!!! It really makes no difference!

The vehicle is acting against the resistance of the conveyor flowing in the opposite direction. If the vehicle's only applying the same amount of force forwards, it will never actually gain any forwards velocity in relation to the ground. At best it will only remain stationary on the conveyor. This is basic Newtonian physics. Two equal forces acting on the same object in opposite directions cancel each other out.

If this is not the case, then if the conveyor is moving backwards, how much thrust does the vehicle have to apply in order to remain stationary in relation to the ground? Exactly the same amount as the conveyor is applying, but in the opposite direction! It doesn't matter whether the thrust is being applied by the jet or by the wheels.

If you start the conveyor off going backwards on it's own, then the plane starts moving backwards with it. It has to apply the same amount of force forwards in order to stop itself from moving backwards in relation to the ground. Any more force than this that it applies, registers on the conveyors sensors as forwards velocity of the vehicle (up until that point it's only been registering negative or zero velocity), and according to the puzzle the conveyor would then increase it's own speed backwards to match the forwards velocity.

So say that the conveyor was moving backwards at 5mph, and the vehicle was applying that same amount of force to go forwards. The plane is now 'stationary'. If the plane now tries to apply any more force to make it go at 6mph (and hence 1mph in actual forwards velocity), the conveyor senses this change and applies the same amount backwards and you're back where you started. Both forces acting equally on the same object.

The vehicle would never be able to move forwards!! The conveyor would always match whatever the vehicle did, no matter what speed it was attempting to push forwards at.

So how do you measure the speed of the conveyor? I can only assume it is the distance travelled by a point on the belt over a period of time. So why measure the speed of the vehicle differently? If the belt works just to keep the car/plane stationary then it is violating the rules of the puzzle. The car/plane moves in one direction the belt moves in the other direction, their relative movement is double.

The forces need to supply that movement are irrelevant. The only difference is that the plane will take off and fly as its propulsion system works on the air around it. The car will take off, and as soon as the wheels leave the ground, lose it's propulsion and settle back onto the conveyor.
Guest
QUOTE (sooks+Dec 4 2005, 12:25 AM)
pretty muvch no matter how fast the belt is moving, the plane will take off. the only force resisting it would be the force withing the wheel bearings.

This is simply not correct!

If the only force resisting it is the wheel bearings, then are you saying that the plane itself is weightless?? If that were the case, I could push it along with my little finger.

The jets actually have a lot of resisting force to push against, and not just air, because the plane is very heavy.

It's not weightless, it weighs 200 tonnes. The jets are having to push the full mass of the plane along the conveyor in order to attain speed. The only way the wheels will ever rotate in either direction is by exerting a force on them that is proportional to the amount of weight bearing down on them - i.e. the weight of the plane. Thus, if the conveyor moves backwards, it does not move the wheels backwards but the whole plane.

Yes, I read Rick Durden's explanation on AvWeb, and he makes the same mistake that nearly everyone makes - he assumes that at some point the plane's wheels become free moving. He assumes that the backwards movement of the conveyor is only affecting the wheels and not the plane itself.

If you have a plane rolling along tarmac at 5mph, and you then start pulling the tarmac along in the opposite direction, does it only affect the wheels? Of course not, the plane is still as heavy as it was when it was standing still, it has just as much weight pushing down on the wheels. It affects the mass of the whole plane.

He makes the mistake with this line: "Those wheels are not powered and thus do not push against the belt to accelerate the airplane."

Of course they have to push against it. How does a plane move along on normal ground? The jets are forcing backwards against the air, and the force that is resisting them is the gravity holding the plane down on the ground. The jets are forcing the whole plane (including the wheels, which are part of the plane), along the ground.

He also uses a hovercraft as an example to prove his point - which is complete nonsense!!

All hovercraft use upwards thrust to lift themselves off the ground. At this point the hovercraft is no longer touching anything at all, it's resting on a cushion of air. It's totally weightless! Unlike the plane it would be bearing no weight down on the conveyor whatsoever. So yes, you could run the conveyor as fast as you like and the hovercraft would never move - even if the hovercraft itself was applying ZERO thrust forwards. And yes, you really could push it along with your little finger!

How is this like a 200 tonnes plane sitting on the conveyor belt? When you move the belt backwards the whole plane moves with it. It can never affect just the wheels on it's own.

Believe me, I have posted about this on other forums several months back, and the vast majority of people - including guys with degrees in engineering and physics (and also some who work with plane engineers on a daily basis ) ALL agree that the plane would not fly!
Guest
QUOTE (Sage+Dec 4 2005, 12:25 AM)
If the belt works just to keep the car/plane stationary then it is violating the rules of the puzzle.
I did not say that. I said that the puzzle contradicts itself, because if the belt is moving in the opposite direction at the same speed then it will prevent the plane from moving! No matter how hard you try!

Two forces acting on an object in opposite directions, cancel each other out.
Bloy
QUOTE (Guest+Dec 4 2005, 04:00 PM)
QUOTE (Sage+Dec 4 2005, 12:25 AM)
If the belt works just to keep the car/plane stationary then it is violating the rules of the puzzle.
I did not say that. I said that the puzzle contradicts itself, because if the belt is moving in the opposite direction at the same speed then it will prevent the plane from moving! No matter how hard you try!

Two forces acting on an object in opposite directions, cancel each other out.

...more frivolity...
If the plane is not moving, then how can the belt(conveyor) be moving.? It states that the belt moves in the opposite direction that the plane moves.

Forget the wheels... they simply (whether driven of not) double their rotation.
ixolas
incorrect!! the plane will take off.

the resistance of a wheel is found by a formula something like this: the weight in newtons (1lb equals 4.45 newtons) times actually wheel resistance (usually below 1% or 0.01) times the speed in meters per second (1mph = .45 meters/hour) equals the opposing force.

The force of thrust to move a plane is found by the formula something like: force in newtons is equal to the mass in newtons times speed in meters/hour.

so a plane weighing 1,335,000 newtons (300,000 lbs) times the wheel resistance .01 and then multiplied by the speed of 1 meter/hour (2.2222 miles/hour) has a rolling resistance of 13350 newtons (3,000 lbs) acting against it. So if the ground was moving in the opposite direction at an additional 1 meter/hour this would double the wheel speed and make it an opposing force of 26700 newtons (6000 lbs) acting against it.

But a plane weighing 1,335,000 newtons moving at 1 meter per seconds has a forward force of 1,335,000 newtons.

Therefore the forward force of 1,335,000 newtons minus the rolling resistance of the conveyor going in the oppose direction is 267,000 newtons leaving a forward force of 1,068,000.

lets put it like this.. if you had a completely free moving wheel.. somehow not connected to the frame (lets say opposing magnetic fields), the opposing force applied to the wheel to spin it by the conveyor would be very, very small on the frame.
So adding ball bearings the force applied to the wheel increases but is still not equal to the force applied to the frame.
Adding weight is the same, the force applied to a fully loaded plane is increased, but the force applied to the frame is not equal to the force of the conveyor.
The resisting, opposing force, on the plane will never equal the opposing force applied to the wheels. Therefore the opposing force on the plane by the conveyor will subtract from the forward force but not equal it.

Also keep in mind that the forward motion is produced by the movement of air. The forward thrust of a plane is 2.222mph, and the conveyor is moving oppositely at 2.222mph, due to the reduction in resistance by the free moving wheels the plane will feel an opposing force of lets say .56mph but it will not be equal to the actual force of the conveyor therefore it will move forward.

Think of yourself standing on a treadmill holding onto a rope. When you advance buy pulling on the rope the treadmill moves oppositely against the wheels, you feel an opposing force but it is only a fraction of the actual force of the treadmill. The plane taking flight uses the propeller through air to move forward like you would use the rope to move forward. The opposing ground would have an opposing reaction on the wheels, but it would not equal the force of the ground, due to free turning wheels.

Now on the other hand if you had a car in the same situation the car would stay still due to the fact the forward motion of the car is caused by an opposing force to the ground. Therefore if the ground moves oppositely to the wheel then the forward motion cancels. The plane does not use the ground to accelerate therefore the opposing negative action will not cancel.
ixolas
QUOTE (ixolas+Dec 4 2005, 08:14 PM)
Think of yourself standing on a treadmill in rollerblades holding onto a rope. When you advance buy pulling on the rope the treadmill moves oppositely against the wheels, you feel an opposing force but it is.

edit
Bloy
QUOTE (ixolas+Dec 4 2005, 08:14 PM)
Therefore if the ground moves oppositely to the wheel then the forward motion cancels

Are you calling the ground the conveyor? Your key words here "oppositely to the wheel". Did you forget that the posed question has in it "opposite to the plane(winged vehicle)" I don't see anything in there about opposite to the wheel. The conveyor moves opposite to the plane(or car) so the wheels spin twice as fast to compensate for the conveyor canceling out the "normal"? rotation of the wheel.
...again. the belt cannot move and cancel out the plane'(car's) forward movement
...no forward movement, then NO conveyor(opposite) movement.

and more frivolity! sooner or later I'm going to stop checking into this thread
twiddly-dee (formerly 'Guest
lol, I suspect the only reason you're still here is beacuse you're still not 100% convinced.

I said that "the belt is moving in the opposite direction at the *same* speed.." meaning at the same speed as whatever the plane is moving forwards at.

Obviously, if the plane is not moving forwards then the belt is not moving backwards. This is exactly what the puzzle implies.

Where the confusion lies is in the puzzle's wording that "the plane moves". This is the contradiction. People take it for granted that plane can actually go forwards.

By saying that the belt measures any movement forwards and counteracts it, it means that if the plane moves in one direction then it also gets moved in the opposite direction by the same amount!

Therefore the plane doesn't really 'move' at all! It's a completely non-sensical question!

It's like a tug-o-war with both teams pulling the same rope in opposing directions. If the left team isn't pulling, then the right team isn't pulling either.

As soon as the left team pulls, it's immediately met by an equal tug by the other team.

No matter how much force is applied by either team, if the other team responds with equal force then the rope always remains still and hence neither would ever win!

I entirely agree with your statement about the wheels though. They simply add to the confusion and make things appear more complicated than they really are. The amount they are rotating is completely irrelevant, what matters is the amount of force being applied to them in both directions.
twiddly-dee
QUOTE (ixolas+Dec 4 2005, 08:14 PM)
The plane does not use the ground to accelerate therefore the opposing negative action will not cancel.

This is the thing I have a problem with.

The plane is sitting on the ground. It has to overcome it's own weight on the ground if it's going to move forwards. It has nothing to do with air. So it must have to push itself along the ground in order to go anywhere! How can the plane not be accelerating itself against the ground?!

What happens in a car: the engine turns the driveshaft, the driveshaft turns the axles, the axles turn the wheels.

What happens in a plane: the jet pushed the chassis, the chassis pushes the axles, the axles turn the wheels.

What's the difference??? Thrust is thrust! It makes no difference where the energy is coming from, they both have the same effect in that they force the wheels of this heavy vehicle to turn against the floor!

What happens if you erect a huge sail on top of the plane/car, and generate your thrust from the wind? Still exactly the same thing!

If you still don't believe me, then imagine this test:

Sit a plane on the conveyor and a car just in front of it. Start the conveyor going backwards at 10mph. Both the car and the plane start travelling back with it. Now start up the engines of both the car and the plane, and ease both the throttles forwards so both the speedometers on the car and plane rise up to 10mph. Does the plane overshoot the car? 10mph is 10mph, no matter what kind of vehicle you're in.

Now reset the experiment, and try doing it again with the conveyor running backwards at 50mph this time.

It's no different to doing the same experiment on normal ground! If both the car and the plane are exerting the same amount of thrust, they will both be travelling at the same speed forwards! There's never any such thing as free wheeling of the plane.

This is simple relativity. The vehicle only acts in relation to the object it's sitting at rest on.

Dont' forget that we ourselves are sitting 'at rest' on a planet which is rotating itself at several thousands of miles per hour, just like the conveyor. Does this affect planes more than it affects cars?

It affects all things equally!
Bloy
So I say... without adding any elements to the posed question.

Will the airprop driven plane reach liftoff speed? Yes
Will the winged wheel driven car/plane reach liftoff speed? yes

Will the airprop driven plane fly?: Yes, because it can continue to accelerate.

Will the winged wheel driven car/plane fly?: NO, because it will lose thrust when friction to the runway is lost at liftoff speed, thus never being able to accelerate beyond the liftoff speed.

That's my final answer and I'm sticking to it.
j6p
"I STAND ON SHOULDERS OF GIANTS WHO POSTED BEFORE ME AND I SEE THE PLANE FLY." quote j6p circa 2005

It was earlier stated that if someone were on a a skate board on a tread mill and tied a rope to the bar, pulled on the rope they would advance forward. The tread mill would exactly match the speed of the wheels but you would still advance forward.
From this I've determined if the plane is powered but the wheels run free then the plane will be able to advance forward and take off.
The trick in the question that bends the mind is:
QUOTE
This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).

The conveyor can only match the speed of the wheels not the speed of the plane. The conveyor powers the wheels and the plane's engine powers the plane. They are connected but they are two independent systems.
ixolas
QUOTE (Bloy+Dec 4 2005, 10:13 PM)
Are you calling the ground the conveyor?  Your key words here "oppositely to the wheel".    Did you forget that the posed question  has in it "opposite to the plane(winged vehicle)" I don't see anything in there about  opposite to the wheel.  The conveyor moves opposite to the plane(or car) so the wheels spin twice as fast to compensate for the conveyor canceling out the "normal"? rotation of the wheel.
...again. the belt cannot move and cancel out the plane'(car's) forward movement
...no forward movement, then NO conveyor(opposite) movement.

The flaw in your argument is that when the plane move forward, relative to the world, the conveyor cancels this. The plane creates a thrust buy moving air thus creating movement. The ground (or conveyor) moves in an opposite direction equal to the forward movement of the plane but like stated previously the force created on the plane by the equal speed of the conveyor, it is always less than the forward thrust of the plane by the movement of the air.

QUOTE (twiddly-dee+Dec 4 2005)
It's like a tug-o-war with both teams pulling the same rope in opposing directions. If the left team isn't pulling, then the right team isn't pulling either.

Incorrect because they are pulling different ropes. The plane is pulling air's rope and the conveyor is pulling on the ropes attached to the ground the planes wheels are on, these aren't the same ropes.

QUOTE (twiddly-dee+Dec 4 2005)
What happens in a plane: the jet pushed the chassis, the chassis pushes the axles, the axles turn the wheels.

grossly incorrect. That is like saying when I stand in Rollerblades on a treadmill and pull on a rope I achieve forward motion through the wheels and not pulling on the rope.

A forward motion in a car is when the wheel pushes against the pavement.
A forward motion in a plane is when the propellers pushes against the air.

QUOTE (Bloy-dee+Dec 4 2005)
Will the winged wheel driven car/plane reach liftoff speed? yes

sorry but no.. wheel driven acceleration acts directly against the ground (or treadmill) and is met with an equal and opposite force therefore canceling any movement.
swimmer
Imagine a swimming pool with conveyer belt bottom. If you're floating at one end and start swimming towards the other, it doesn't matter if the bottom of the pool starts to shoot away in the opposite direction. You will continue to swim/move relative to the water and reach the other end.

So getting back to the plane on the conveyer belt - the wheels on the landing gear are there to minimise friction with the ground. That's all they do. The plane's engines provide thrust relative to the air, not the ground.

The plane in air is like the swimmer in water. It doesn't matter whether the bottom of the pool or the conveyer belt is moving in the opposite direction to the swimmer or plane. The medium through which the plane flies or the swimmer swims is the key.
Bloy
QUOTE (ixolas+Dec 5 2005, 02:15 AM)
QUOTE (Bloy+Dec 4 2005, 10:13 PM)
Are you calling the ground the conveyor?  Your key words here "oppositely to the wheel".    Did you forget that the posed question  has in it "opposite to the plane(winged vehicle)" I don't see anything in there about  opposite to the wheel.  The conveyor moves opposite to the plane(or car) so the wheels spin twice as fast to compensate for the conveyor canceling out the "normal"? rotation of the wheel.
...again. the belt cannot move and cancel out the plane'(car's) forward movement
...no forward movement, then NO conveyor(opposite) movement.

The flaw in your argument is that when the plane move forward, relative to the world, the conveyor cancels this. The plane creates a thrust buy moving air thus creating movement. The ground (or conveyor) moves in an opposite direction equal to the forward movement of the plane but like stated previously the force created on the plane by the equal speed of the conveyor, it is always less than the forward thrust of the plane by the movement of the air.

The flaw in YOUR reasoning is that when the plane moves relative to the "universe", the conveyor equals it oppositely.... not cancels it.

So I say...again... without adding any elements to the posed question.

Will the airprop driven plane reach liftoff speed? Yes
Will the winged wheel driven car/plane reach liftoff speed? yes

Will the airprop driven plane fly?: Yes, because it can continue to accelerate.

Will the winged wheel driven car/plane fly?: NO, because it will lose thrust when friction to the runway is lost at liftoff speed, thus never being able to accelerate beyond the liftoff speed.

That's still my final answer and I'm sticking to it.
sooks
QUOTE (j6p+Dec 5 2005, 12:30 AM)
"I STAND ON SHOULDERS OF GIANTS WHO POSTED BEFORE ME AND I SEE THE PLANE FLY." quote j6p circa 2005

It was earlier stated that if someone were on a a skate board on a tread mill and tied a rope to the bar, pulled on the rope they would advance forward. The tread mill would exactly match the speed of the wheels but you would still advance forward.
From this I've determined if the plane is powered but the wheels run free then the plane will be able to advance forward and take off.
The trick in the question that bends the mind is:
QUOTE
This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).

The conveyor can only match the speed of the wheels not the speed of the plane. The conveyor powers the wheels and the plane's engine powers the plane. They are connected but they are two independent systems.

j6p....precisely right. thats why the plane takes off and the car stands still
ixolas
THE PLANE WILL ACHIEVE FLIGHT!

QUOTE (Bloy+Dec 5 2005, 03:29 AM)
The flaw in YOUR reasoning is that when the plane moves relative to the "universe", the conveyor  equals it oppositely....  not cancels it.

If the plane creates a forward force equal to make the plane move forward at 1 mph relative to the earth the conveyor moves in the opposite direction at 1 mph?
If the plane creates a forward force equal to make the plane move forward at 5 mph relative to the earth the conveyor moves in the opposite direction at 5 mph?
If the plane creates a forward force equal to make the plane move forward at 100 mph relative to the earth the conveyor moves in the opposite direction at 100 mph?

So therefore as previously stated the movement of the conveyor moving in the opposite direction at same spead of the plane would not create enough opposing force to keep the plane from moving forward.

Newtons Third law (for every action there is an equal and opposite action) is why you are thinking the plane won't move. But the acting force in the plane is the propellers and not the wheels.

let me ask you this, If there was a car on a paved road and the wind was blowing in an opposing direction equal to the forward movement of the car, would the car move?

The car gains forward motion by applying a force through the tires against the ground. The tires act against the ground to move the car forward, the wind blowing in the opposite direction as the car in the equal amount of speed, does contact the car and slow it down but does not act on the direct force applied to the ground by the tires. The car acts against the ground to create forward motion and the opposing equal speed of the wind acts against the car but will be less than the force the car creates against the ground.

The plane gains forward motion by applying a force through the propellers against the air. The propellers act against the air to move the plane forward, the ground moving in the opposite direction as the plane in the equal amount of speed, does contact the planes tires and slow it down but does not act on the direct force applied to the air by the propellers. The plane acts against the air to create forward motion and the opposing equal speed of the ground movement acts against the plane but will be less than the force the plane creates against the air.
Bloy
[QUOTE=sooks,Dec 5 2005, 03:44 AM] [/QUOTE]

The conveyor can only match the speed of the wheels not the speed of the plane. The conveyor powers the wheels and the plane's engine powers the plane. They are connected but they are two independent systems.
[/QUOTE]
Huh?
The conveyor powers nothing... it only moves oppositely and equally to the movement of the plane(or wheel driven winged plane. If the plane moves 50MPH, then the conveyor moves oppositely 50MPH. Rev the powered wheels up so the translated rpms of the wheels is twice that of the 50mph conveyor (100mph if you MUST look at the speedometer that is correctly calibrated to give speed at "normal "operation without the conveyor) and you achieve
a speed of 50mph(of the winged wheel driven plane). If this is the liftoff speed of the wheel driven winged plane, the friction will start to degrade. Never mind the conveyor speeding up to cancel the wheel rotation, it is going to stay at the forward speed of the wheel driven winged plane...if not, then it is not tracking the speed of the wheel driven winged plane properly.

So I say...again... without adding any elements to the posed question.

Will the airprop driven plane reach liftoff speed? Yes
Will the winged wheel driven car/plane reach liftoff speed? yes

Will the airprop driven plane fly?: Yes, because it can continue to accelerate.

Will the winged wheel driven car/plane fly?: NO, because it will lose thrust when friction to the runway is lost at liftoff speed, thus never being able to accelerate beyond the liftoff speed. If this conveyor/runway is finite, it would be time to apply brakes

That's still my final answer and I'm sticking to it.
sooks
QUOTE (Bloy+Dec 5 2005, 04:28 AM)
[QUOTE=sooks,Dec 5 2005, 03:44 AM] [/QUOTE]

The conveyor can only match the speed of the wheels not the speed of the plane. The conveyor powers the wheels and the plane's engine powers the plane. They are connected but they are two independent systems.
[/QUOTE]
Huh?
The conveyor powers nothing... it only moves oppositely and equally to the movement of the plane(or wheel driven winged plane. If the plane moves 50MPH, then the conveyor moves oppositely 50MPH. Rev the powered wheels up so the translated rpms of the wheels is twice that of the 50mph conveyor (100mph if you MUST look at the speedometer that is correctly calibrated to give speed at "normal "operation without the conveyor) and you achieve
a speed of 50mph(of the winged wheel driven plane). If this is the liftoff speed of the wheel driven winged plane, the friction will start to degrade. Never mind the conveyor speeding up to cancel the wheel rotation, it is going to stay at the forward speed of the wheel driven winged plane...if not, then it is not tracking the speed of the wheel driven winged plane properly.

So I say...again... without adding any elements to the posed question.

Will the airprop driven plane reach liftoff speed? Yes
Will the winged wheel driven car/plane reach liftoff speed? yes

Will the airprop driven plane fly?: Yes, because it can continue to accelerate.

Will the winged wheel driven car/plane fly?: NO, because it will lose thrust when friction to the runway is lost at liftoff speed, thus never being able to accelerate beyond the liftoff speed. If this conveyor/runway is finite, it would be time to apply brakes

That's still my final answer and I'm sticking to it.

Well...i guess i dont have much else to debate it with you wiht the car winged thingy. other than the fact that it just isnt logical like i was saying before for it to be matching car speed. what j6p was saying made sense as it doesnt match the car speed. it doesnt make sense or i cant even think of a way that it could do that..... the logic becomes circular when trying to think of a way to match that speed relative to the earth. what he was saying in terms of the belt powers the wheels....is they dont exactly power the wheels, but the frictional force between the belt and the wheels is what turns them....
Ylleks
QUOTE (sooks+Dec 5 2005, 05:23 AM)
QUOTE (sooks+Dec 5 2005, 03:44 AM)

The conveyor powers nothing... it only moves oppositely and equally to the movement of the plane(or wheel driven winged plane.  If the plane moves 50MPH, then the conveyor moves oppositely 50MPH.

But here's where you run into a problem. How do you determine what the conveyors movement speed is, if the car is traveling 50 mph?

Lets say you have a conveyor belt, and you place an object on it. If the conveyor belt is moving 50 MPH, how far will that object have moved in 1 hour? Would it not be 50 miles?

Therefore, if the car is travelling 50 mph relative to a ground observer, then what is the conveyor travelling at relative to a ground observer? If they are both traveling at 50 mph, then the car has not travelled 50 miles, thus it's not really travelling 50 mph.

It appears the car's speed determines the conveyor's speed, and the conveyor's speed also affects the car's speed. But the plane speed determines the conveyor speed, but the conveyor speed does not affect the plane's speed.

In order for this problem to be true, I state no, the plane will not take off, because it's relative ground speed must be 0.
j6p
Thanks sooks for straightening that out for me, of course I don't think the wheels are powered by anything. They are spun/turned/rotated by the conveyor.
Swimmer
QUOTE (Guest+Dec 4 2005, 03:54 PM)

Believe me, I have posted about this on other forums several months back, and the vast majority of people - including guys with degrees in engineering and physics (and also some who work with plane engineers on a daily basis ) ALL agree that the plane would not fly!

All that proves is people can pass exams without actually understanding their subject!

The plane's engines move the plane relative to the air not the ground.

The wheels on the under carriage are there to minimise friction with the ground while the plane is on the ground.

Visit an airport some time and you'll see planes easily produce enough thrust to accelerate their mass and overcome the friction with the ground. So mass, inertia and friction are not an issue in this puzzle. The key is to examine the initial conditions.

The plane is not moving, the conveyer belt is not moving, the air is not moving. Switching on the engines provides forward thrust against the air. The thrust overcomes both inertia and friction in the system. If the conveyer belt moves in the opposite direction at the same speed as the plane, all that does is make the wheels rotate at twice their usual rate.

Think of a swimmer in a pool with a conveyer belt bottom. As soon as the swimmer sets off from one end, the conveyer moves in the opposite direction. Are you really saying this swimmer would stay in the same place because of the conveyer belt at the bottom of the pool? Of course not. The swimmer provides thrust against the water and moves relative to the water.

No doubt you're now going to say "yes but he's floating" - it makes no difference.

Imagine the pool is shallow and the swimmer is touching the bottom. Place some wheels under him to minimise the friction between the swimmer and the pool bottom. The swimmer moves relative to the water. Whatever effect the conveyer belt bottom has is minimal because the friction between swimmer and the bottom of the pool is minimal.

If you still don't get it - imagine you are wearing a pair or rollerskates and you're standing still on a conveyer belt which isn't moving and you are holding a rope tied to a distant tree. You start to pull on the rope with sufficient force to pull you forward at 5mph. The conveyer belt instantly moves at 5mph in the opposite direction. Does that stop you moving closer to the tree? NO. You continue to move at 5mph and the wheels rotate at the equivalent of 10mph.
Guest
QUOTE (Swimmer+Dec 5 2005, 04:16 PM)
Think of a swimmer in a pool with a conveyer belt bottom. As soon as the swimmer sets off from one end, the conveyer moves in the opposite direction. Are you really saying this swimmer would stay in the same place because of the conveyer belt at the bottom of the pool? Of course not. The swimmer provides thrust against the water and moves relative to the water.

...

If you still don't get it - imagine you are wearing a pair or rollerskates and you're standing still on a conveyer belt which isn't moving and you are holding a rope tied to a distant tree. You start to pull on the rope with sufficient force to pull you forward at 5mph. The conveyer belt instantly moves at 5mph in the opposite direction. Does that stop you moving closer to the tree? NO. You continue to move at 5mph and the wheels rotate at the equivalent of 10mph.

A better analogy would be to imagine swimming upstream on a river. If the faster you swim, the faster the current flows against you, you'll never get anywhere.

Like swimming against the tide if you're out at sea. If the tide's going out at the same rate you're swimming forwards, you'll never get back to land.

Now attach a jetpack to your back, pushing against the air above the water. Again, the smallest movement forwards through the water and the current still pushes you back where you came from, at exactly the same speed.

Also with the thing about pulling yourself along a rope on a conveyor. I take it you're assuming the tree itself is standing on the ground beside the conveyor...? If so, this is wrong because the plane itself never has any contact with any object on the ground. Everything it does is only relative to the object it's sitting on - the conveyor.

Try placing the tree on the conveyor itself and see what happens. Does it stop you from pulling yourself towards the tree? No. Does it stop you from going forwards in relation to the ground? Yes. Because any distance you pull yourself forwards, both you and the tree are pushed back at the same rate by the conveyor.

ixolas
QUOTE (Guest+Dec 5 2005, 06:21 PM)

A better analogy would be to imagine swimming upstream on a river. If the faster you swim, the faster the current flows against you, you'll never get anywhere.

Like swimming against the tide if you're out at sea. If the tide's going out at the same rate you're swimming forwards, you'll never get back to land.

Now attach a jetpack to your back, pushing against the air above the water. Again, the smallest movement forwards through the water and the current still pushes you back where you came from, at exactly the same speed.

Also with the thing about pulling yourself along a rope on a conveyor. I take it you're assuming the tree itself is standing on the ground beside the conveyor...? If so, this is wrong because the plane itself never has any contact with any object on the ground. Everything it does is only relative to the object it's sitting on - the conveyor.

Try placing the tree on the conveyor itself and see what happens. Does it stop you from pulling yourself towards the tree? No. Does it stop you from going forwards in relation to the ground? Yes. Because any distance you pull yourself forwards, both you and the tree are pushed back at the same rate by the conveyor

no it is not because.
when you are swiming you push against water and if the water was floawing oppositely then you would be applying force to the opposing force.

When a plane takes flight it pushes against the air and not the ground moving oppositely.
If the anagaly was if a plane tries to take flight and the wind blew with the opposing force would it fly? no it wouldn't cause the air is what the plane is acting against not the ground!!!

the analagy IS similar to standing on a treadmill and pulling on a rope because you are acting against the rope to acheive forward movement like the plane is pulling on the air to acheive forward movement even if the treadmill is moving at the equal opposite speed.
sooks
QUOTE (Ylleks+Dec 5 2005, 02:19 PM)
QUOTE (sooks+Dec 5 2005, 05:23 AM)
QUOTE (sooks+Dec 5 2005, 03:44 AM)

The conveyor powers nothing... it only moves oppositely and equally to the movement of the plane(or wheel driven winged plane.   If the plane moves 50MPH, then the conveyor moves oppositely 50MPH.

But here's where you run into a problem. How do you determine what the conveyors movement speed is, if the car is traveling 50 mph?

Lets say you have a conveyor belt, and you place an object on it. If the conveyor belt is moving 50 MPH, how far will that object have moved in 1 hour? Would it not be 50 miles?

Therefore, if the car is travelling 50 mph relative to a ground observer, then what is the conveyor travelling at relative to a ground observer? If they are both traveling at 50 mph, then the car has not travelled 50 miles, thus it's not really travelling 50 mph.

It appears the car's speed determines the conveyor's speed, and the conveyor's speed also affects the car's speed. But the plane speed determines the conveyor speed, but the conveyor speed does not affect the plane's speed.

In order for this problem to be true, I state no, the plane will not take off, because it's relative ground speed must be 0.

You make sense, and what you are saying is true. Im not debating that fact with any of you now... all im saying is that it is impossible for the belt to measure the speed with relation to the ground. the car is moving 50 mph compared to the belt... more like as soon as the car makes motion relative to the belt not the ground.....then the belt matches that movement.
Guest
Did I miss this yet? The plane will not fly because the engines will not generate lift. The engines will generate thrust, but not lift. Since the plane is not moving relative to the atmosphere, there will be no air flow to generate lift.
Guest
QUOTE (ixolas+Dec 5 2005, 06:35 PM)
If the anagaly was if a plane tries to take flight and the wind blew with the opposing force would it fly? no it wouldn't cause the air is what the plane is acting against not the ground!!!

Sir, you know nothing about aerodynamics!! The more wind blowing against the aircraft from the front the easier it is for the plane to fly!!

More air flowing backwards over the wings means more lift. Why do you think passenger planes always turn into the wind to take off?!

http://science.howstuffworks.com/airplane8.htm

If a plane needs to be travelling at 100mph in order to take off, this has nothing to do with it's groundspeed, it simply means it needs 100mph of wind blowing over the wings to generate lift. Even if the plane is standing still on the tarmac, if you blow 100mph of wind over it's wings it will take off just like a kite.
Guest
QUOTE (Guest+Dec 5 2005, 08:08 PM)
Did I miss this yet? The plane will not fly because the engines will not generate lift. The engines will generate thrust, but not lift. Since the plane is not moving relative to the atmosphere, there will be no air flow to generate lift.

Engines don't generate lift. Wings generate lift.

But you're right -- the engines will generate thrust. That means the plane will move forward, regardless of what the ground is doing. An airplane's wheels freewheel. They're always in neutral. The engines aren't pushing on the ground, so it makes no difference what the ground is doing. The plane rolls forward regardless, but the wheels spin faster.

Let's think about the opposite case. I have a little Cessna -- small airplane, doesn't need much speed to take off. My takeoff speed is maybe 50 knots.

Imagine my little Cessna facing into a stiff wind. The wind flows over the wings, though the ground is not moving. I run my engine to counter the force of the wind, which would otherwise drive my airplane backward. The wind gets faster and faster -- at fifty knots, the wings are producing fifty knots' worth of lift, and my Cessna can rise off the ground, going straight up without the wheels turning an inch! Now, the engine is running just as fast as if I were flying fifty miles per hour through calm air, but the wheels didn't turn at all.

This is the same problem, approached from the other direction. The treadmill-runway is only spinning the tires. The engines feel the force of the wind, and that's all. The wings feel the force of the wind, and that's all. The counter-movement of the treadmill doesn't do anything, because all the operating parts of the airplane are moving air around and acting on air -- the wheels are just there to spin!
Guest
It's like a guy with a jetpack and rollerskates on a treadmill. The treadmill doesn't do anything to the jetpack -- it's sucking in air and blowing it out the back, not spinning the wheels.
Guest
I think the question is malformed. I think the question was designed so that "If a plane is not moving, but its engines are active, will it be able to take off?" would be its true intention.

Right now, we are not given any information about the conveyor belt. For all we know, this 777 or Airbus whatever could be on a 2 meter runway. The moment the plane starts moving, it will veer off the conveyor belt, and crash, thereby killing everyone on board.
Guest
You say that the wheels are free spinning, and the conveyor only spins the wheels back.

What happens if you try to spin the plane's wheels with your own hands? Can you spin them? No, because of the weight of the plane bearing down on them.

Even if you did have the strength to turn one of them, would it just spin round on it's own? No, it would force the plane back.

Try doing it on your own car with the handbrake off. Can you spin the wheel without pushing the car back? You seem to be forgetting that gravity affects the whole vehicle, which includes the wheels. The heavier the vehicle, the more difficult it is to turn the wheels.
Guest
But it should be true that there is some acceleration in speed a which the belt can have that will stop the plane from taking off.
Sage
QUOTE (Guest+Dec 5 2005, 09:47 PM)
I think the question is malformed. I think the question was designed so that "If a plane is not moving, but its engines are active, will it be able to take off?" would be its true intention.

Right now, we are not given any information about the conveyor belt. For all we know, this 777 or Airbus whatever could be on a 2 meter runway. The moment the plane starts moving, it will veer off the conveyor belt, and crash, thereby killing everyone on board.

So the question does not fit your answer therefore the question is wrong?

At least you made me smile.
charlied
this problem is written 2 different ways around the inet

"Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyor belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.

This one and your question are similar but different.
In the above question it states " match the speed of the wheels in the opposite direction of rotation" to me this means the conveyor keeps the wheels stationary by moving at the same speed and direction as the plane so the plane flys but the wheels never turn.

In your question it states "opposite direction", in that case the wheel bearings would have to have as much friction as the planes engines have power, not going to happen. The tires fly off and the plane takes off on wheels
Guest
QUOTE (Sage+Dec 5 2005, 10:11 PM)
QUOTE (Guest+Dec 5 2005, 09:47 PM)
I think the question is malformed. I think the question was designed so that "If a plane is not moving, but its engines are active, will it be able to take off?" would be its true intention.

Right now, we are not given any information about the conveyor belt. For all we know, this 777 or Airbus whatever could be on a 2 meter runway. The moment the plane starts moving, it will veer off the conveyor belt, and crash, thereby killing everyone on board.

So the question does not fit your answer therefore the question is wrong?

At least you made me smile.

Absolutely! But agree with me here, the original question never describes the viability of the conveyor belt. If the conveyor belt is not suitable as a runway, then the plane cannot take off. The way the question is phrased suggests that it is intended that the plane cannot move.
sooks
QUOTE (Guest+Dec 5 2005, 10:18 PM)
QUOTE (Sage+Dec 5 2005, 10:11 PM)
QUOTE (Guest+Dec 5 2005, 09:47 PM)
I think the question is malformed. I think the question was designed so that "If a plane is not moving, but its engines are active, will it be able to take off?" would be its true intention.

Right now, we are not given any information about the conveyor belt. For all we know, this 777 or Airbus whatever could be on a 2 meter runway. The moment the plane starts moving, it will veer off the conveyor belt, and crash, thereby killing everyone on board.

So the question does not fit your answer therefore the question is wrong?

At least you made me smile.

Absolutely! But agree with me here, the original question never describes the viability of the conveyor belt. If the conveyor belt is not suitable as a runway, then the plane cannot take off. The way the question is phrased suggests that it is intended that the plane cannot move.

I dont get why so many people just assume the plane cant move. Where in the question does it say the plane cant move...all its saying is the conveyor is moving in the opposite direction as fast as the plane is... People are making it way more difficult than it is..... yes it could be worded more throughly. but why on earth would someone imagine the runway is 2 m long. it is supposed to be somewaht misleading...thats why its somewhat of a brain teaser, and thats why people are posting it...cause your natural instinct is to think it wont move.
Sage
QUOTE (Ylleks+Dec 5 2005, 02:19 PM)
QUOTE (sooks+Dec 5 2005, 05:23 AM)
QUOTE (sooks+Dec 5 2005, 03:44 AM)

The conveyor powers nothing... it only moves oppositely and equally to the movement of the plane(or wheel driven winged plane.   If the plane moves 50MPH, then the conveyor moves oppositely 50MPH.

But here's where you run into a problem. How do you determine what the conveyors movement speed is, if the car is traveling 50 mph?

Lets say you have a conveyor belt, and you place an object on it. If the conveyor belt is moving 50 MPH, how far will that object have moved in 1 hour? Would it not be 50 miles?

Therefore, if the car is travelling 50 mph relative to a ground observer, then what is the conveyor travelling at relative to a ground observer? If they are both traveling at 50 mph, then the car has not travelled 50 miles, thus it's not really travelling 50 mph.

It appears the car's speed determines the conveyor's speed, and the conveyor's speed also affects the car's speed. But the plane speed determines the conveyor speed, but the conveyor speed does not affect the plane's speed.

In order for this problem to be true, I state no, the plane will not take off, because it's relative ground speed must be 0.

By your example, the car will not be travelling at 50mph relative to a ground observer, it will be stationary so the conditions are not met.

Take a long conveyor (say 1000miles), Glue a little dinky toy mini to a spot at one end of the conveyor so that this toy moves exactly at the same rate of the belt. Fly up to the other end of the conveyor (we all mostly agree now that the plane will fly) and get into your real life MINI. Let's imagine that this super-conveyor has a big dial which we can use to control the speed of it. Lastly imagine that there is a lamp-post located every mile along it's length.

Now,
1. Start the MINI and accelerate to 50mph then set the cruise control - our speed over the belt isn't going to change. For now the conveyor is switched off and not moving. At this rate we (in the MINI) will pass 50 lamp-posts in 1 hour.

2. Now switch on the conveyor at turn the speed dial to 10mph. Our toy will start moving at 10mph (ie it will pass 10 lampposts in 1 hour). The MINI is still travelling at 50mph along the belt but our motion past the lamp-posts is reduced to 40 lamp-posts per hour due to the motion of the belt. Agreed? So far so good.

3. Increase the dial to 20 mph. Our toy mini now moves passed 20 lamp-posts an hour. Our relative speed is still the same but now in our real MINI we will only pass 30 lamp-posts per hour due to the motion of the belt.

4. Now what would happen if we cranked the dial up to 25mph? Our speed relative to the belt remains 50mph. Our speed in one direction is 25mph (sorry, lamp-posts per hour), the toy mini's speed in the other direction is 25 lamp-posts per hour.

This is the only scenario that fits the criteria of the puzzle, ie the car is moving & the belt and car move in opposite directions at the same speed.

To say that the belt will move at 50 mph to keep the car stationary is as wrong as saying that the car moves at 50mph whist the belt remains stationary...and no-one is (yet) advocating this point of view.
Sage
QUOTE (charlied+Dec 5 2005, 10:14 PM)
this problem is written 2 different ways around the inet

"Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyor belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.

This one and your question are similar but different.
In the above question it states " match the speed of the wheels in the opposite direction of rotation" to me this means the conveyor keeps the wheels stationary by moving at the same speed and direction as the plane so the plane flys but the wheels never turn.

In your question it states "opposite direction", in that case the wheel bearings would have to have as much friction as the planes engines have power, not going to happen. The tires fly off and the plane takes off on wheels

Worded this way the puzzle is non-sensical. Certainly a car would go nowhere.

Can't get my head round the plane though. Engines produce thrust to push plane along the ground. But the plane must remain in contact with the ground until take-off speed. Therefore the wheels must turn, but belt matches wheel rotation so plane stays still. Friction of tyres must surely be overcome by the engine thrust?

Either plane stays still which seems impossible given thrust is forcing it to move through the air. Or thrust reaches a point where is simply shreds the tyres along the runway, probably the undercarriage will collapse and the belly of the plane will scrape along the runway until the pilot has the sense to switch off the engines. It will move but I can't see it being in a state to fly. Doesn't fit so neatly, if wheels speed and belt speed are the same it becomes a bit messy when the thrust just takes over regardless.

I'd bet that ours is the more original wording, it's a much neater puzzle - this version is a corruption (probably puT out by someone who thinks the plane can't fly, but I would say that, wouldn't I?)
ixolas
QUOTE (Guest+Dec 5 2005, 08:33 PM)
QUOTE (ixolas+Dec 5 2005, 06:35 PM)
If the anagaly was if a plane tries to take flight and the wind blew with the opposing force would it fly? no it wouldn't cause the air is what the plane is acting against not the ground!!!

Sir, you know nothing about aerodynamics!! The more wind blowing against the aircraft from the front the easier it is for the plane to fly!!

I am just trying to prove a point that planes push against air and not the ground therefore the conveir wouldn't be much of a factor.
Ane if you would read what i said
QUOTE (ixolas+Dec 5 2005, 06:35 PM)
If the anagaly was if a plane tries to take flight and the wind blew with the opposing force would it fly? no it wouldn't cause the air is what the plane is acting against not the ground!!!

I didn't say against the plane i said in an opposing force! which means if there was some other propeller spinning in a equally opposite direction directly in front of the planes propeller the opposing forces would cancel, or an opposing equal tailwind.

I am totally and completely aware of how planes fly and completely aware of the physics of this question. I am trying to explain to others in some other way to help them understand.

You running on a treadmill at the same speed as the treadmill will not move forward because with each step you push off of the treadmill that is opposing you.

A car driving on a conveyor at the same speed as the conveyor will not move forward because the tires push off of the treadmill that is opposing it.

A boat driving in a stream at the same speed as the stream will not move forward because the propellers push off the moving water that is opposing it.

A plane spinning its propellers on a conveyor would move forward because the proppellers push off the air that is not part of the opposing conveyor movement.
ixolas
ok let me ask you this..

If a there was a large lake and the entire bottom of the lake was a moving conveyor. Only the ground not the water! And you had a boat that can't float and is supported by legs that at the end were free turning wheels. Would the boat move when the on-board v8 turns the propellers in the water? Even if the little wheels that support it are turning in the equal opposite way?

If a plane is flying through the air at a constant 100 mph and there is a train moving in the opposite direction at 100 mph and the plane keeping a constant 100 mph flew just over it and the wheels barely touched the train would the plane come to a complete stop just by touching the wheels to the train? Why not? The train is moving at 100 mph in the exact opposite way just like the conveyor?

The fact is that most people want to picture this like a car on a conveyor and you can't. You have to think of it like yourself on a treadmill in Rollerblades pulling a rope. The air the plane pulls against (or pushes against) is completely different than the conveyor turning the little wheels it sits on.
Guest
QUOTE (ixolas+Dec 5 2005, 11:49 PM)
If a plane is flying through the air at a constant 100 mph and there is a train moving in the opposite direction at 100 mph and the plane keeping a constant 100 mph flew just over it and the wheels barely touched the train would the plane come to a complete stop just by touching the wheels to the train? Why not? The train is moving at 100 mph in the exact opposite way just like the conveyor?

No, of course the train would not stop. And neither would it push the plane back either.

What would happen is, as the plane's wheels came into contact with the roof of the train, they would spin very fast (at 200mph) because the train is only pushing them backwards and not the plane itself......

So you're saying, why doesn't the same thing apply when the plane's on the ground....?

THIS is the big difference. When the plane is flying, it has overcome it's own gravity and it's totally weightless. When it's sitting stationary on the ground, it's nowhere near weightless.

If the train was moving in the same direction as the plane, and you were standing on the roof of the train as the plane came down to meet you, you could literally spin the wheels yourself with your own hands. And you could even grab hold of the axles and lift the plane up and down in the air with one arm. The plane is weightless!

So say that the plane now lands on the train and switch it's engines off. Can you lift the plane now? Or rotate the wheels on their own?

Gravity and relativity.

So yep, when the wheels touch the train moving in the opposite direction it ONLY moves the wheels, not the plane. But this ain't so on the ground.

Take these three jet-skis:

http://thegrapevine.brinkster.net/js3.jpg

They are all identical in weight. The only differences are the ones indicated - one has a jet underwater, one over it, and one has a propellor. Drop them on a calm lake, and at full speed each of them achieves a maximum speed of 3 mph.

Now drop them on a river facing upstream into the current. Does any one of the jet skis move any faster than the other?

If the one with the jet outside the water moves any better against the current than the other two, then why don't all boats have jets above the water?

sooks
QUOTE (Guest+Dec 6 2005, 12:54 AM)
QUOTE (ixolas+Dec 5 2005, 11:49 PM)
If a plane is flying through the air at a constant 100 mph and there is a train moving in the opposite direction at 100 mph and the plane keeping a constant 100 mph flew just over it and the wheels barely touched the train would the plane come to a complete stop just by touching the wheels to the train? Why not? The train is moving at 100 mph in the exact opposite way just like the conveyor?

No, of course the train would not stop. And neither would it push the plane back either.

What would happen is, as the plane's wheels came into contact with the roof of the train, they would spin very fast (at 200mph) because the train is only pushing them backwards and not the plane itself......

So you're saying, why doesn't the same thing apply when the plane's on the ground....?

THIS is the big difference. When the plane is flying, it has overcome it's own gravity and it's totally weightless. When it's sitting stationary on the ground, it's nowhere near weightless.

If the train was moving in the same direction as the plane, and you were standing on the roof of the train as the plane came down to meet you, you could literally spin the wheels yourself with your own hands. And you could even grab hold of the axles and lift the plane up and down in the air with one arm. The plane is weightless!

So say that the plane now lands on the train and switch it's engines off. Can you lift the plane now? Or rotate the wheels on their own?

Gravity and relativity.

So yep, when the wheels touch the train moving in the opposite direction it ONLY moves the wheels, not the plane. But this ain't so on the ground.

Take these three jet-skis:

http://thegrapevine.brinkster.net/js3.jpg

They are all identical in weight. The only differences are the ones indicated - one has a jet underwater, one over it, and one has a propellor. Drop them on a calm lake, and at full speed each of them achieves a maximum speed of 3 mph.

Now drop them on a river facing upstream into the current. Does any one of the jet skis move any faster than the other?

If the one with the jet outside the water moves any better against the current than the other two, then why don't all boats have jets above the water?

they dont make jet ski'is like that because they arent as efficient. it takes more power to move the distance. air doesnt provide as much resistance as water or ground does.
ixolas
QUOTE (Guest+Dec 6 2005, 12:54 AM)
No, of course the train would not stop. And neither would it push the plane back either.

What would happen is, as the plane's wheels came into contact with the roof of the train, they would spin very fast (at 200mph) because the train is only pushing them backwards and not the plane itself......

So yep, when the wheels touch the train moving in the opposite direction it ONLY moves the wheels, not the plane. But this ain't so on the ground.

Ok.. you've almost got my point.. my point is that the conveyor pushes on the wheels and not the plane itself. The engines (ie the turbines or propellers) pushes the plane forwards and the conveyor pushes the wheels and not the plane itself.

Now granted the equal opposing movement of the conveyor against the wheels would cause alot of friction and slow down the plane but the conveyor is turning the wheels and the plane only feels a fraction of this force.

what about my boat in water with wheels on the conveyor? what about that?
sooks
QUOTE (ixolas+Dec 6 2005, 01:23 AM)
QUOTE (Guest+Dec 6 2005, 12:54 AM)
No, of course the train would not stop. And neither would it push the plane back either.

What would happen is, as the plane's wheels came into contact with the roof of the train, they would spin very fast (at 200mph) because the train is only pushing them backwards and not the plane itself......

So yep, when the wheels touch the train moving in the opposite direction it ONLY moves the wheels, not the plane. But this ain't so on the ground.

Ok.. you've almost got my point.. my point is that the conveyor pushes on the wheels and not the plane itself. The engines (ie the turbines or propellers) pushes the plane forwards and the conveyor pushes the wheels and not the plane itself.

Now granted the equal opposing movement of the conveyor against the wheels would cause alot of friction and slow down the plane but the conveyor is turning the wheels and the plane only feels a fraction of this force.

what about my boat in water with wheels on the conveyor? what about that?

if you guys want to compare examples with boats and water and streams......hree are pretty much identical examples to the plane and car.

the plane is the same as a fan boat going up stream.....it moves teh same as going downstream water has no effect.

the car is the same as a prop boat...if its going up stream it has a huge affect. and if its going upstream 10mph and the stream is going 10mph... its stationary
Guest
QUOTE (ixolas+Dec 6 2005, 01:23 AM)

Now granted the equal opposing movement of the conveyor against the wheels would cause alot of friction and slow down the plane

The conveyor and the wheels are moving in the same direction. No opposing force what-so-ever.

The plane takes off even faster than it normally would. The conveyor would actually act to reduce the normal friction a plane experiences on take-off. The weight of the plane and the effort it takes to get the wheels moving against the ground in order to get the plane up to take-off speed. The conveyor moving in the same direction as the wheels would be helpful in this regard.
Bloy
Sooks said:
"the car is the same as a prop boat...if its going up stream it has a huge affect. and if its going upstream 10mph and the stream is going 10mph... its stationary "
--------------------------------------------------------------------------------------------
You are saying the the car and boat are both going 10mph..yet they are stationary? quite a contradiction with basic laws. ... hmmmm you have really bent the rules to suit your vision.

One has to stick to one reference point. I've seen it here in this thread going from the wheels, to the conveyor, the ground , the atmosphere, the world, the grass along the runway, the bottom of the pool, the water in the pool, the current of a river, etc. etc.

Stationary to what? the trees along the shore? I'm standing next to that tree and I don't see any boat in the water stream going 10mph. I hear an engine in a boat driving a prop, but it is not running the boat at 10mph. In fact it's not moving, so I see it as going 0mph. So I shout to the boat pilot: "give it more throttle!" and the boat begins to go upstream at 10mph as the increased engine rpms drive the prop faster. I ask loudly over the roar of the engine: "What does your speedometer read!" The boat pilot translates knots into mph and replies back with a yell over the noises: "It says 20mph!"

If it is going upstream at 10mph then that is what speed it is going upstream. the stream(current) could be a waterfall....but the vehicle is going up stream at 10mph whatever the stream is doing.
Guest
QUOTE (Guest (from yesterday)+Aug 30 2005, 03:38 PM)
Wright Brother,
What is the exhaust pushing against to give the thrust if it is not the air? If it were a true vacuum how would you achieve thrust if the exhaust gasses hit nothing? There would be no reaction to the action of the gasses exiting the engine.
The pros use air jets and rocket engines in space but space is not a true vacuum and has lots of stuff floating around in it to be pushed against.
I don't mean to sound belittling but I may have a misunderstanding and want to clear it up.

Woah, I have to address this here.

Imagine you are sitting in a rolling office chair with a bunch of heavy weights. Throw one of those weights against the wall and you will move backwards. Now, turn and throw the weight out the window -- you still move backwards although the weight didn't hit anything.

Jet engines, rockets, and balloons that have been let go all fly forward due to a release of gas, but none of them push against air. If this were true, rockets would have much poorer performance in space, but this is not true at all. They are essentially throwing air molecules backwards, and it doesn't matter if those air molecules hit anything.

All these things fly based conservation of momentum. Newton's law of motion: every action has an equal and opposite reaction. The jet, rocket, or balloon somehow accelerates a gas rapidly backwards, and to conserve momentum, it must move forwards.

In fact, if you took your jet and modified it so that instead of pulling in air from the atmosphere it pulled in air from a tank, and then put it in a vacuum, it would still move forwards, because the momentum of the air escaping backwards must be equal and opposite to the momentum of the plane moving forwards.
twiddly-dee
QUOTE (sooks+Dec 6 2005, 02:31 AM)

if you guys want to compare examples with boats and water and streams......hree are pretty much identical examples to the plane and car.

the plane is the same as a fan boat going up stream.....it moves teh same as going downstream water has no effect.

How can you say the water has no effect on the fanboat? That completely defies the laws of physics.

OK, so say the fanboat is facing downstream and is applying no thrust, but the river itself is moving at a speed of 5mph. How fast is the fanboat moving? It's moving downstream at 5mph, same as the river. The river is carrying the weight of the fanboat downstream. Now what happens if you apply 5mph of thrust on the fanboat (so his speedo reads 5mph)? It's now moving downstream at 10mph. The thrust of the fanboat PLUS the speed of the river gives the total velocity in relation to the riverbank. Right?

The fanboat itself stills weighs the same as it did when it was applying no thrust. And thus, is still being acted upon by the flow of the river in exactly the same manner.

Now turn the fanboat round so it's facing upstream. Again, applying no thrust on the fanboat, if the river is flowing at 5mph then the fanboat must be moving backwards 5mph in relation to the riverbank. Apply 5mph of thrust and the fanboat (so his speedo says 5mph), it is now moving 0mph. 5mph forwards plus MINUS 5mph backwards means the fanboat is now not moving in relation to the riverbank.

So whether it's a fan above water or a prop below it, it makes zero difference. Can you agree with that?

If the physics applies the one way then it must apply the other.
sooks
QUOTE (twiddly-dee+Dec 6 2005, 10:52 AM)
QUOTE (sooks+Dec 6 2005, 02:31 AM)

if you guys want to compare examples with boats and water and streams......hree are pretty much identical examples to the plane and car.

the plane is the same as a fan boat going up stream.....it moves teh same as going downstream water has no effect.

How can you say the water has no effect on the fanboat? That completely defies the laws of physics.

OK, so say the fanboat is facing downstream and is applying no thrust, but the river itself is moving at a speed of 5mph. How fast is the fanboat moving? It's moving downstream at 5mph, same as the river. The river is carrying the weight of the fanboat downstream. Now what happens if you apply 5mph of thrust on the fanboat (so his speedo reads 5mph)? It's now moving downstream at 10mph. The thrust of the fanboat PLUS the speed of the river gives the total velocity in relation to the riverbank. Right?

The fanboat itself stills weighs the same as it did when it was applying no thrust. And thus, is still being acted upon by the flow of the river in exactly the same manner.

Now turn the fanboat round so it's facing upstream. Again, applying no thrust on the fanboat, if the river is flowing at 5mph then the fanboat must be moving backwards 5mph in relation to the riverbank. Apply 5mph of thrust and the fanboat (so his speedo says 5mph), it is now moving 0mph. 5mph forwards plus MINUS 5mph backwards means the fanboat is now not moving in relation to the riverbank.

So whether it's a fan above water or a prop below it, it makes zero difference. Can you agree with that?

If the physics applies the one way then it must apply the other.

Yes, the water does have some affect, but its minimal. much the same as wheels on a conveyor belt...yes there is frictional force, but is nearly negligible compared to the power of the engines...
Bloy
QUOTE (sooks+Dec 6 2005, 02:35 PM)
[QUOTE=sooks,Dec 6 2005, 02:31 AM]

Yes, the water does have some affect, but its minimal. much the same as wheels on a conveyor belt...yes there is frictional force, but is nearly negligible compared to the power of the engines...

Sooks, what are you trying to prove here? Are you trying to understand yet why things work the way they do? What is your question? Are you refuting that the car, plane, boat, truck, air or wheel(prop) driven will move forward?
I'm trying to figure out what you want us to question?
Bloy
QUOTE (Bloy+Dec 6 2005, 02:50 AM)
Sooks said:
"the car is the same as a prop boat...if its going up stream it has a huge affect. and if its going upstream 10mph and the stream is going 10mph... its stationary "
--------------------------------------------------------------------------------------------

Bloy replies:

You are saying the the car and boat are both going 10mph..yet they are stationary?  quite a contradiction with basic laws. ... hmmmm you have really bent the rules to suit your vision.

One has to stick to one reference point.  I've seen it here in this thread going from the wheels, to the conveyor, the ground , the atmosphere, the world, the grass along the runway, the bottom of the pool, the water in the pool, the current of a river, etc. etc.

Stationary to what? the trees along the shore?  I'm standing next to that tree and I don't see any boat in the water stream going 10mph.  I hear an engine in a boat driving a prop, but it is not running the boat at 10mph.  In fact it's not moving, so I see it as going 0mph.  So I shout to the boat pilot: "give it more throttle!" and the boat begins to go upstream at 10mph (My trusty radar detector indicates so) as the increased engine rpms drive the prop faster.  I ask loudly over the roar of the engine: "What does your speedometer read!"  The boat pilot translates knots into mph and replies back with a yell over the noises: "It says 20mph!"

If it is going upstream at 10mph then that is what speed it is going upstream.  the stream(current) could be a waterfall....but the vehicle is going up stream at 10mph whatever the stream is doing.

sooks
QUOTE (Bloy+Dec 6 2005, 02:57 PM)
QUOTE (Bloy+Dec 6 2005, 02:50 AM)
Sooks said:
"the car is the same as a prop boat...if its going up stream it has a huge affect. and if its going upstream 10mph and the stream is going 10mph... its stationary "
--------------------------------------------------------------------------------------------

Bloy replies:

You are saying the the car and boat are both going 10mph..yet they are stationary?  quite a contradiction with basic laws. ... hmmmm you have really bent the rules to suit your vision.

One has to stick to one reference point.  I've seen it here in this thread going from the wheels, to the conveyor, the ground , the atmosphere, the world, the grass along the runway, the bottom of the pool, the water in the pool, the current of a river, etc. etc.

Stationary to what? the trees along the shore?  I'm standing next to that tree and I don't see any boat in the water stream going 10mph.  I hear an engine in a boat driving a prop, but it is not running the boat at 10mph.  In fact it's not moving, so I see it as going 0mph.  So I shout to the boat pilot: "give it more throttle!" and the boat begins to go upstream at 10mph (My trusty radar detector indicates so) as the increased engine rpms drive the prop faster.  I ask loudly over the roar of the engine: "What does your speedometer read!"  The boat pilot translates knots into mph and replies back with a yell over the noises: "It says 20mph!"

If it is going upstream at 10mph then that is what speed it is going upstream.  the stream(current) could be a waterfall....but the vehicle is going up stream at 10mph whatever the stream is doing.

I dont really have a question. i was just responding to other peoples questions. The one guy was asking how the stream couldnt affect the fan boat. From your second post you just had, yes i realized, i didnt word that one all that well... moving 10 mph relative to the stream. much as the car's speed is relative to the belt. I was saying any ground driven mode of transport wont move, any air driven transport will.
Guest
So if you have a prop-driven boat and a fan-driven boat of identical weight, both powering downstream at 10mph, and then without altering the throttle both pilots swing their boats round to face the opposite direction - you're saying the fan-boat somehow starts powering ahead of the prop driven one?

Do you realize how rediculous that is?!
sooks
QUOTE (Guest+Dec 6 2005, 05:53 PM)
So if you have a prop-driven boat and a fan-driven boat of identical weight, both powering downstream at 10mph, and then without altering the throttle both pilots swing their boats round to face the opposite direction - you're saying the fan-boat somehow starts powering ahead of the prop driven one?

Do you realize how rediculous that is?!

yes it will...granted not that much because the resistance of all th water through the entire hull is a lot of friction.... much more than a wheel to the conveyor belt. Meaning drag has much more of an impact than in the conveyor belt problem. Look, its only an example, it isnt perfect. Im just saying its as close as your getting to explain the car and belt vs plane and belt situation.
Guest
The best example would be:

A car and plane are rolling along normal tarmac, side by side, at identical speeds. After a couple of miles, they run onto a wide travellator (like the ones you walk along at the airport), travelling in the same direction they're travelling, at 5mph.

After a few miles the travellator finishes and they carry on back along the tarmac again.

After a few more miles they run onto another travellator, travelling in the opposite direction this time, again at 5mph.

After this travellator finishes they are back on tarmac again, and they have reached their destination so they both come to a stand still.

Does the car finish before the plane, or the plane before the car?
sooks
QUOTE (Guest+Dec 6 2005, 09:04 PM)
The best example would be:

A car and plane are rolling along normal tarmac, side by side, at identical speeds. After a couple of miles, they run onto a wide travellator (like the ones you walk along at the airport), travelling in the same direction they're travelling, at 5mph.

After a few miles the travellator finishes and they carry on back along the tarmac again.

After a few more miles they run onto another travellator, travelling in the opposite direction this time, again at 5mph.

After this travellator finishes they are back on tarmac again, and they have reached their destination so they both come to a stand still.

Does the car finish before the plane, or the plane before the car?

well althogh this works....its not really a separate example...but pretty much the same question just a different viewpoint...and yes the plane would get there first.

Try this example. your on a treadmill and your on roller blades. infront of you is a rope attached to a tree..... the treadwill move as fast as your wheels..... so your staying in position untill you pull on that rope you will actually move forward.
Guest
QUOTE (sooks+Dec 6 2005, 09:43 PM)
[QUOTE=Guest,Dec 6 2005, 09:04 PM]and yes the plane would get there first.

Try this example. your on a treadmill and your on roller blades. infront of you is a rope attached to a tree..... the treadwill move as fast as your wheels..... so your staying in position untill you pull on that rope you will actually move forward.

I don't see how pulling a rope fixed to a stationary object relates to a jet....but anyways....

If the plane finishes first, at what point does it overtake the car - the tarmac, the forwards travellator, or the backwards travellator?
swimmer
QUOTE (Guest+Dec 5 2005, 06:21 PM)
QUOTE (Swimmer+Dec 5 2005, 04:16 PM)
Think of a swimmer in a pool with a conveyer belt bottom. As soon as the swimmer sets off from one end, the conveyer moves in the opposite direction. Are you really saying this swimmer would stay in the same place because of the conveyer belt at the bottom of the pool? Of course not. The swimmer provides thrust against the water and moves relative to the water.

...

If you still don't get it - imagine you are wearing a pair or rollerskates and you're standing still on a conveyer belt which isn't moving and you are holding a rope tied to a distant tree. You start to pull on the rope with sufficient force to pull you forward at 5mph. The conveyer belt instantly moves at 5mph in the opposite direction. Does that stop you moving closer to the tree? NO. You continue to move at 5mph and the wheels rotate at the equivalent of 10mph.

A better analogy would be to imagine swimming upstream on a river. If the faster you swim, the faster the current flows against you, you'll never get anywhere.

Like swimming against the tide if you're out at sea. If the tide's going out at the same rate you're swimming forwards, you'll never get back to land.

Now attach a jetpack to your back, pushing against the air above the water. Again, the smallest movement forwards through the water and the current still pushes you back where you came from, at exactly the same speed.

Also with the thing about pulling yourself along a rope on a conveyor. I take it you're assuming the tree itself is standing on the ground beside the conveyor...? If so, this is wrong because the plane itself never has any contact with any object on the ground. Everything it does is only relative to the object it's sitting on - the conveyor.

Try placing the tree on the conveyor itself and see what happens. Does it stop you from pulling yourself towards the tree? No. Does it stop you from going forwards in relation to the ground? Yes. Because any distance you pull yourself forwards, both you and the tree are pushed back at the same rate by the conveyor.

No offence but please don't tell me you're an engineer or a physicist!

The plane derives forward thrust by pushing on the AIR. Ok?
The AIR - not the ground - not the conveyer belt - not the wheels - only the AIR.

In my stupid rope-pulling-rollerskater analogy the distant tree (growing in the ground by the way) represents the air that the plane pushes against.

The conveyer belt has no effect on the air - so your analogy of a guy swimming upstream against currents or tides is irrelevant. Think about it.
swimmer
QUOTE (Guest+Dec 6 2005, 05:53 PM)
So if you have a prop-driven boat and a fan-driven boat of identical weight, both powering downstream at 10mph, and then without altering the throttle both pilots swing their boats round to face the opposite direction - you're saying the fan-boat somehow starts powering ahead of the prop driven one?

Do you realize how rediculous that is?!

Well somethings ridiculous here but it's not the fact that the fan-driven boat will go faster upstream than the propeller-driven one!

In fact in the above example - if the river current were 5mph, once headed upstream the propeller-driven boat would stay in the same place relative to the river bank while the fan-driven boat would continue upstream at 5mph. (ignoring friction)

Why? - because the fan-driven boat derives thrust relative to the air above the river and the prop-driven boat derives thrust relative to the water in the river.
Guest
QUOTE (swimmer+Dec 6 2005, 11:02 PM)

Why? - because the fan-driven boat derives thrust relative to the air above the river and the prop-driven boat derives thrust relative to the water in the river.

OK, please explain why the fan-driven boat doesn't travel any faster than the prop boat when heading *downstream* or on calm water.....?

It's still deriving it's thrust relative to the *air above the water*, no matter which direction you're facing....

If the resistance of the water somehow affects a fan-boat less, then if it's travelling downstream, surely this must provide some extra thrust as the boat is now moving *with* the flow, not against it....?

If what you're saying's true, and fans are more efficient than propellors, why don't all boats have fans? Then they could turn the props off when heading upstream and turn the fans on because it 'makes them travel faster'.....

Why do you only see boats like this with engines and props, and not fans or jets?

And surely this extra speed would be crucial in saving lives on sea rescue boats that have to travel against tides.

And yet.....they all have props, or jets beneath the water.....
sooks
QUOTE (Guest+Dec 7 2005, 12:27 AM)
QUOTE (swimmer+Dec 6 2005, 11:02 PM)

Why? - because the fan-driven boat derives thrust relative to the air above the river and the prop-driven boat derives thrust relative to the water in the river.

OK, please explain why the fan-driven boat doesn't travel any faster than the prop boat when heading *downstream* or on calm water.....?

It's still deriving it's thrust relative to the *air above the water*, no matter which direction you're facing....

If the resistance of the water somehow affects a fan-boat less, then if it's travelling downstream, surely this must provide some extra thrust as the boat is now moving *with* the flow, not against it....?

If what you're saying's true, and fans are more efficient than propellors, why don't all boats have fans? Then they could turn the props off when heading upstream and turn the fans on because it 'makes them travel faster'.....

Why do you only see boats like this with engines and props, and not fans or jets?

And surely this extra speed would be crucial in saving lives on sea rescue boats that have to travel against tides.

And yet.....they all have props, or jets beneath the water.....

Thank you swimmer, was starting feel kinda lonely out here . I think you are explaining it better than me too.

in response to the guests response. The fan boat wont be going any faster than the prop boat because it isnt being held back. if anything it would be going faster than the fan boat. if both were going the same speed in perfectly calm water. then without adjusting throttle, they hit a downstream current. the boat would gain more speed from the current while the fan boat would be unexpected........ if they hit an upstream current, the boat would slow down while the fan boat remained constant. Basically what im saying is that the current is virtually (there are some effects of friction) irrelevant.

The reason that there are more propellor boats is cause the fan boats arent more efficient. And most boats are not designed for river's. it takes more power from the engine to push the air to create movement then it does for a prop in the water to push it. because water is heavier and pushing more water creates more propulsion than does the fan in the air. and as far as using them as saving time.... they do use a personal hover craft in oceans for rescues. its mostly because they can go out across the sand and into the water...but also because it is easier once it hits water going out against the tide.
Justin
*** Brain Teaser ***

Imagine an airplane is on the beginning of a massive conveyor belt, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.

Can the plane take off?

JUSTIN
Duh
Because there's to much drag on the drive shaft that connects to the wheels!
Bloy
QUOTE (Justin+Dec 7 2005, 06:41 PM)
*** Brain Teaser ***

Imagine an airplane is on the beginning of a massive conveyor belt, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.

Can the plane take off?

JUSTIN

Before answering, is the conveyor matching the "rotational" speed of the wheels? That is..... the circumference of the wheel travels at the same speed as the belt of the conveyor. OR, are you talking of the lateral movement of the wheels. That is...the wheel unit actually moves its axle from one point to another in a given time matching the belt movement oppositely.

....just so confusion is at a minimum....
sooks
QUOTE (Bloy+Dec 7 2005, 08:18 PM)
QUOTE (Justin+Dec 7 2005, 06:41 PM)
*** Brain Teaser ***

Imagine an airplane is on the beginning of a massive conveyor belt, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.

Can the plane take off?

JUSTIN

Before answering, is the conveyor matching the "rotational" speed of the wheels? That is..... the circumference of the wheel travels at the same speed as the belt of the conveyor. OR, are you talking of the lateral movement of the wheels. That is...the wheel unit actually moves its axle from one point to another in a given time matching the belt movement oppositely.

....just so confusion is at a minimum....

haha....oh no, are we starting all over again...
sooks
QUOTE (Bloy+Dec 7 2005, 08:18 PM)
QUOTE (Justin+Dec 7 2005, 06:41 PM)
*** Brain Teaser ***

Imagine an airplane is on the beginning of a massive conveyor belt, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.

Can the plane take off?

JUSTIN

Before answering, is the conveyor matching the "rotational" speed of the wheels? That is..... the circumference of the wheel travels at the same speed as the belt of the conveyor. OR, are you talking of the lateral movement of the wheels. That is...the wheel unit actually moves its axle from one point to another in a given time matching the belt movement oppositely.

....just so confusion is at a minimum....

Bloy,

I totally get what you have been saying about comparing to the ground and how its different measuring wheel speed and car speed. and speed is distance/time. It all makes sense. But, where i have my problem with that. Is that in the context of the problem, can you explain to me how its logically possible that the belt would be able to match that speed? That is where i have the problem, to me it becomes circular logic that the belt cannot measure.
Guest_Jeff
No it will never take off you idiots. Like someone told me earlier today try running on a tread mill with a kite and see if it flies. It will not. No wind equals no lift. The air being sucked into the engines does not create enough wind flowing over the wings to create lift. So even though the thrust of the jets will move the plane forward they will not give it the desired result of air passing over the wings. IT WON'T FLY. I know they say there are no stupid question, but they probably haven't seen this one.
sooks
QUOTE (Guest_Jeff+Dec 7 2005, 08:48 PM)
No it will never take off you idiots. Like someone told me earlier today try running on a tread mill with a kite and see if it flies. It will not. No wind equals no lift. The air being sucked into the engines does not create enough wind flowing over the wings to create lift. So even though the thrust of the jets will move the plane forward they will not give it the desired result of air passing over the wings. IT WON'T FLY. I know they say there are no stupid question, but they probably haven't seen this one.

Excuse me guest_jeff idiot. Before you go off calling people names and sounding like a complete moron yourself, why dont you try to learn a little bit about something before smarting off at the mouth. Perhaps if you even looked at more than 1 page of this entire thread you would have learned the science behind it. NOWHERE in the problem does it say the plane cannot move. That is the question that we're debating is whether or not it can accelerate. everyone knows you need wind to create lift, so in order to get that wind it must move..... were debating whether or not it will move... not if it can take off stationary. (which could be possible with about a 200mph headwind by the way). Which i think the good majority of us came to the decision that it would move and accelerate and thus acheive lift. It is UNLIKE the running on a treadmill example because you power your legs and use friction of the ground to move...unlike the plane which pushes against the air with thrust to move forward. it would move without wheels. the wheels and belt are negligible. So do a little research next time and you wouldnt have wasted my time expaining to you why your a moron.
Bloy
hehe heh....hmmm I'm thinking of something else to feed the smoldering fire....

Maybe someone will be the lucky 500th reply.....
sooks
QUOTE (Bloy+Dec 7 2005, 09:42 PM)
hehe heh....hmmm I'm thinking of something else to feed the smoldering fire....

haha....sorry, i dont care if someone disagrees with me. But if theyre going to be rude about it or ignorant and cant come across respectful, they better not expect it back.
Bloy
That's right Sooks..... there is no need to start bashing with names and the likes...... any comment is welcome as long as it is respectful.....otherwise just view and move on.
No one can fault others taking this thread and all its nuances to a different avenue of thought.
sooks
QUOTE (Bloy+Dec 7 2005, 09:47 PM)
That's right Sooks..... there is no need to start bashing with names and the likes...... any comment is welcome as long as it is respectful.....otherwise just view and move on.
No one can fault others taking this thread and all its nuances to a different avenue of thought.

Thanks bloy, completely agree.

Did you get a chance to see the question i was asking you about the ground matching speed? its a few posts back right before my rant. I just see it mathmatically working, but the logic doesnt fit in my head.
Quest Master Genius
Hey retardo-s.
Try taking some BRAIN pills, re-res
The problem CLEARLY states the plane WON'T fly.
The PLANE moves on the TREADMILL which takes the place of GROUND
The PLANE moves over ground at 500 MPH
The PLANE will moves over the TREADMILL at 500 MPH
If the TREADMILL moves at 500 MPH, then the PLANE will NOT move compared to the ground.

Try taking some physics classes and come back when you are older than 14, kiddos
sooks
QUOTE (Quest Master Genius+Dec 7 2005, 10:12 PM)
Hey retardo-s.
Try taking some BRAIN pills, re-res
The problem CLEARLY states the plane WON'T fly.
The PLANE moves on the TREADMILL which takes the place of GROUND
The PLANE moves over ground at 500 MPH
The PLANE will moves over the TREADMILL at 500 MPH
If the TREADMILL moves at 500 MPH, then the PLANE will NOT move compared to the ground.

Try taking some physics classes and come back when you are older than 14, kiddos

hey "genius" (kinda ironic...) if the wheels are dependent on motion of the plane.... how come a plane with floats will take off on water...or on skis on ice... the wheels are INDEPENDENT and will simply just spin faster the faster the treadmill spins but not impeded forward motion.... I figured a genius would be able to figure that out...but maybe not. Why dont you take a few more classes, go learn what a free body diagram is and see which forces are acting on it. I mean honestly, how old are you... i dont think anyone over the age of 17 calls people "retardo-s" wihtout sounding like one yourself. Really, just take a step back and figure out your mistakes and then hide your head in shame.
sooks
In case your still the "genious" you claim to be and guest-jeff your so smart that were wrong.... try looking at this link and then please come back to me and tell me im wrong.

http://www.avweb.com/news/columns/191034-1.html
Sage
QUOTE (sooks+Dec 7 2005, 10:23 PM)
QUOTE (Quest Master Genius+Dec 7 2005, 10:12 PM)
Hey retardo-s.
Try taking some BRAIN pills, re-res
The problem CLEARLY states the plane WON'T fly.
The PLANE moves on the TREADMILL which takes the place of GROUND
The PLANE moves over ground at 500 MPH
The PLANE will moves over the TREADMILL at 500 MPH
If the TREADMILL moves at 500 MPH, then the PLANE will NOT move compared to the ground.

Try taking some physics classes and come back when you are older than 14, kiddos

hey "genius" (kinda ironic...) if the wheels are dependent on motion of the plane.... how come a plane with floats will take off on water...or on skis on ice... the wheels are INDEPENDENT and will simply just spin faster the faster the treadmill spins but not impeded forward motion.... I figured a genius would be able to figure that out...but maybe not. Why dont you take a few more classes, go learn what a free body diagram is and see which forces are acting on it. I mean honestly, how old are you... i dont think anyone over the age of 17 calls people "retardo-s" wihtout sounding like one yourself. Really, just take a step back and figure out your mistakes and then hide your head in shame.

Don't bite Sooks, these guys are just sent to test us.....even the name is a clue. Master Quest Genius = anagram of Amusing Queer Tests?

Best response is no response, leave him to troll somewhere else.
STILL master SMARTEST
QUOTE (sooks+Dec 7 2005, 10:28 PM)
In case your still the "genious" you claim to be and guest-jeff your so smart that were wrong.... try looking at this link and then please come back to me and tell me im wrong.

http://www.avweb.com/news/columns/191034-1.html

IT'S YOU'RE NOT YOUR

MAYBE YOU SHOULD TAKE SOME ENGLISH CLASES ALONG WITH THOSE PHYSICS CLASSES. SIGH, THE PUBLIC SCHOOL SYSTEM FAILS US ONCE MORE.

Bloy
QUOTE (Quest Master Genius+Dec 7 2005, 10:12 PM)
Hey retardo-s.
Try taking some BRAIN pills, re-res
The problem CLEARLY states the plane WON'T fly.
The PLANE moves on the TREADMILL which takes the place of GROUND
The PLANE moves over ground at 500 MPH
The PLANE will moves over the TREADMILL at 500 MPH
If the TREADMILL moves at 500 MPH, then the PLANE will NOT move compared to the ground.

Try taking some physics classes and come back when you are older than 14, kiddos

hee hee.... this ones WAY out there!.... he should take some flying lessons....

It's usually the most arogant ones who name themselves as brilliant!
Tim the Hermit
Despite his rude way of putting it, Quest Master Genius is right.

The conveyor takes place of the ground, and anything that happens on the treadmill happens exactly as it would do on the ground. And the ground itself becomes irrelevant.

Whichever way the conveyor moves, it carryies the plane in that direction.

Just like an aircraft carrier carries planes. This is why aircraft carriers always travel forwards and into the wind when the planes take off. It makes it easier for them to fly.

If they were moving in the opposite direction it does the opposite, and makes it harder to fly.

So if the carrier were travelling in the opposite direction, at the same speed the plane needs to take off, it would never get to take off.

That's the maths they teach you at flight school.
Bloy
QUOTE (Tim the Hermit+Dec 7 2005, 11:27 PM)
Despite his rude way of putting it, Quest Master Genius is right.

The conveyor takes place of the ground, and anything that happens on the treadmill happens exactly as it would do on the ground. And the ground itself becomes irrelevant.

Whichever way the conveyor moves, it carryies the plane in that direction.

Just like an aircraft carrier carries planes. This is why aircraft carriers always travel forwards and into the wind when the planes take off. It makes it easier for them to fly.

If they were moving in the opposite direction it does the opposite, and makes it harder to fly.

So if the carrier were travelling in the opposite direction, at the same speed the plane needs to take off, it would never get to take off.

That's the maths they teach you at flight school.