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Fynlcut
QUOTE (Guest+Feb 8 2006, 05:13 PM)
Take the conveyor belt and tires out of the equation since the force by each one of them cancels the other out. The plane sits in one spot.

The jet engine on a passenger plane sits under the wing which sucks in air and expells it behind the wings.

The air the engine is sucking is funneled through the engine and not under the wings.

The plane needs air traveling at a certain speed under the wings to cause lift.

The plane does not take off.

The only way it could take off is if the engines were able to suck in a 200 mph wall of air and the only way they could do that is if they were powered by a HEMI.

Surely you jest
Guest
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.
Guest
QUOTE (Atl5p+Dec 8 2005, 10:40 PM)

Ok, here goes...your 'Prop' is pulling a 'column' of air....that column is exactly the same circumfrence as the prop....and it extends in front of the plane into infinity.

That column of air is the *ONLY 'air'* that the prop is affecting. So, when you crank up the engine to make the plane go 10 mph for taxi, the "Prop" is pulling that column of air at 10mph. Since the prop is connected to the engine, to the fuseloge, to the landing gear, to the wheels, things begin to happen. The wheels move in relation to the ground, which (on a calm wind day) is moving at the same speed as the air (0 mph). Thus, the forward motion of the wheels in relation to the ground causes the rest of the plane to move forward in relation to the stationary air which surrounds the wings at 10mph.

Then you crank up the belt to -10 mph. The 'Prop' is still pulling the air in it's column at 10mph. The prop is still connected to the engine, to the fuseloge, to the landing gear, to the wheels. But now the belt is moving at -10mph. The Prop's column of air is also moving at 10mph. The plane continues to travel over the gound (belt) at 10 mph, but the belt is moving 'backwards' in relation to the calm wind. Thus the forces are negated, and the plane seems to 'stand still' in relation to the tower.

Remember, the prop only acts upon that 'column' of air directly in front of it. It has nothing to do with the air to the 'sides' as in the air over the wings.

There's your physics....the prop is acting on an imaginary column of air that is directly in front of the prop, and it extends forward into infinity....that column of air is the exact circumfrence as the prop itself.
Guest
I believe I DO understand the question....there are just many folks out here that don't have much common sence.

The prop is not causing the air to travel over the wings...the prop is just pulling a 'cylinder' of air...displacing it from 'in front' of the plane to 'the back' of the plane.

That force causes an equal and opposite action on the rest of the plane, causing it to move forward in relation to the ground it is sitting on.

When the plane is at rest, the only other force acting on the plane is gravity, which is 'sticking' the plane to the ground. If the ground is 'stationary', then the plane moves forward through the air. Conversly, if the ground is 'moving backwards' as in a tread mill, all forward motion reletive to the tower is negated. Thus no air moves across the wings, thus there is NO LIFT.

I understand where the 'It will Fly' people are going wrong...they are assuming that all the air is physically connected. If you pull the cylinder of air via the prop, then you believe that 'all the air around the plane' will start to move as well....this is backwards.

What is really happening is the prop is moving a horizontal column of air...normally that causes the plane to move in relation to the ground...it's THIS movement that causes the calm air surrounding the ground to become attacked by the wing.

However, when the 'ground' is moving backwards, all forward momentum is stopped, thus no lift.
sooks
wow..teh last two statements were simply amazing...

wrong.

to teh first guest.. you were pretty close to right... but when you said the plane is pulling the air at 10mph.. belt is at 10 mph.. then the plane is doing 10 mph.. and the wheels are doing 20. if the plane is pulling 10 mph worth of air..it has to move forward 10 mph... if it was standing still where is that air being pushed being lost?? the belt cannot exert hardly any force onto the plane.

the second guest... your still thinking of it like a car.. a plane doesnt achieve motion through the ground.. it acts like i just explained above. draw a stupid free body diagram if you still cant see it.
krreagan
QUOTE (Guest+Feb 8 2006, 11:35 AM)
I believe I DO understand the question....there are just many folks out here that don't have much common sence.

The prop is not causing the air to travel over the wings...the prop is just pulling a 'cylinder' of air...displacing it from 'in front' of the plane to 'the back' of the plane.

That force causes an equal and opposite action on the rest of the plane, causing it to move forward in relation to the ground it is sitting on.

When the plane is at rest, the only other force acting on the plane is gravity, which is 'sticking' the plane to the ground.  If the ground is 'stationary', then the plane moves forward through the air.  Conversly, if the ground is 'moving backwards' as in a tread mill, all forward motion reletive to the tower is negated.  Thus no air moves across the wings, thus there is NO LIFT.

I understand where the 'It will Fly' people are going wrong...they are assuming that all the air is physically connected.  If you pull the cylinder of air via the prop, then you believe that 'all the air around the plane' will start to move as well....this is backwards.

What is really happening is the prop is moving a horizontal column of air...normally that causes the plane to move in relation to the ground...it's THIS movement that causes the calm air surrounding the ground to become attacked by the wing.

However, when the 'ground' is moving backwards, all forward momentum is stopped, thus no lift.

You may understand the question, you just don't appear to know how to apply the physical concepts to arrive at an acceptable solution!!

The plane generates thrust (force) to move forward. The belt moves in the opposite direction but applies virtually no force on the plane!

1} What force is being used to counter the force from the planes engines?

2} How is this force transfered from the belt to the plane?

Answer both of these and you will have converts! (Hint: Nobody in 270+ pages has been able to do it acceptably!).

Krreagan
Guest
Why do top-fuel drag cars have skinny tires up front? It's because the front tires don't propel the car, the huge rear tires do...the un-driven front tires do nothing but create 'Drag'. So the wider they are, the more 'drag' they create, thus they use 'skinny tires' to reduce this drag as much as possible.

BTW- Didn't they break the land-speed record on TIRES at over Mach1? We've got the same tires on this plane...so nothing 'blows up'....

Tires at high speed create a TON of drag!! This is why they get so HOT. That's why you get V or Z rated tires on your Corvette, because 'T' rated tires are not built to withstand the heat generated by those high speeds.

If it were not for 'Drag', then what is heating up those tires? Tires by themselves cause the friction...it is directly related to the weight of the vehicle wearing those tires.

If you take a 'T' speed rated tire (110mph) and try to run it at 150mph for an extended amount of time, the tires will generate so much heat they will explode.

A 'Z' rated tire (149+mph) is able to withstand the heat, so they can ride very fast without blowing up. Where's all that heat comming from, Kreegan, if not from Friction...friction from the tires themselves rolling along the road....un-driven tires at that
Bloy
QUOTE (Guest+Feb 8 2006, 08:27 PM)
Why do top-fuel drag cars have skinny tires up front? It's because the front tires don't propel the car, the huge rear tires do...the un-driven front tires do nothing but create 'Drag'. So the wider they are, the more 'drag' they create, thus they use 'skinny tires' to reduce this drag as much as possible.

BTW- Didn't they break the land-speed record on TIRES at over Mach1? We've got the same tires on this plane...so nothing 'blows up'....

Tires at high speed create a TON of drag!! This is why they get so HOT. That's why you get V or Z rated tires on your Corvette, because 'T' rated tires are not built to withstand the heat generated by those high speeds.

If it were not for 'Drag', then what is heating up those tires? Tires by themselves cause the friction...it is directly related to the weight of the vehicle wearing those tires.

If you take a 'T' speed rated tire (110mph) and try to run it at 150mph for an extended amount of time, the tires will generate so much heat they will explode.

A 'Z' rated tire (149+mph) is able to withstand the heat, so they can ride very fast without blowing up. Where's all that heat comming from, Kreegan, if not from Friction...friction from the tires themselves rolling along the road....un-driven tires at that

guest, What are you talking about????
Guest
When the rubber is warmed, it get's 'stickier', thus it's able to produce more friction. But when heat is added to a properly inflated tire, the air pressure will increase by a couple psi...making it produce a little less friction.

However, running an improperly inflated tire at high speed will cause too much heat, and the tire will come apart (remember the Firestones on Explorers?). Under normal circumstances they were fine...but if they were just a little underinflated, and a little overloaded, BOOM!

It's a point you refuse to accept. Tires freewheeling on the ground WILL generate heat. The faster you spin them, the more heat is generated. So, the faster you run that treadmill, the more friction you are creating, thus heating up those tires...where is that heat comming from? It's comming from it's efforts to slow the plane down!

Put a a fan on a skateboard, and put that onto a treadmill. Turn on the fan, and then turn on the treadmill...you WILL be able to achieve equilibrium, and the skateboard will appear to 'stand still'.

Go to a skatepark, and right after Tony Hawk gets off the ramp, see how hot those wheels are!!! Not in the bearings...the surface of the wheel...it's hot!!

The friction and the heat build higher and higher as speed increases.
sooks
guest...sure theres friction... .just not nearly enough to negate thrust... i figured on a 747 to be like 10k lbs friction compared to 200k lbs thrust..
Jack
QUOTE (Guest+Feb 8 2006, 06:35 PM)

However, when the 'ground' is moving backwards, all forward momentum is stopped, thus no lift.

I can't believe I am posting here again....

Guest, you are absolutely right. The whole issue can be answered with your simple statement.

I don't understand how Sook can say this is ridiculous, or that you are thinking about it like a car.

Do this for me Sook (at least as a thought experiment) - strap a big fan on your back and some roller skates on your feet.

Now, go out onto a level, smooth street. Turn the fan on high and have your buddy record your speed--that is the speed which your body is moving relative to the ground.

Now, go get on a treadmill and set it to that speed (let's say 10 mph). Leave your rollerskates and your fan on, and make sure the fan is still set to high.

Stick your arms out. Do you feel any wind rushing over/under them?
Jack
QUOTE (Jack+Feb 8 2006, 08:43 PM)
QUOTE (Guest+Feb 8 2006, 06:35 PM)

However, when the 'ground' is moving backwards, all forward momentum is stopped, thus no lift.

I can't believe I am posting here again....

Guest, you are absolutely right. The whole issue can be answered with your simple statement.

I don't understand how Sook can say this is ridiculous, or that you are thinking about it like a car.

Do this for me Sook (at least as a thought experiment) - strap a big fan on your back and some roller skates on your feet.

Now, go out onto a level, smooth street. Turn the fan on high and have your buddy record your speed--that is the speed which your body is moving relative to the ground.

Now, go get on a treadmill and set it to that speed (let's say 10 mph). Leave your rollerskates and your fan on, and make sure the fan is still set to high.

Stick your arms out. Do you feel any wind rushing over/under them?

Oh yeah...forgot to mention one thing.

If you think the air being pushed by the engines generates lift, think again. Those engines (or your fan) generate THRUST, not lift.
sooks
im not denying there isnt friction.. just that thrust is such a bigger force... now your starting say waht i was getting at a page or two ago.. when you try to match the wheel speed. they are going to be spinning faster and faster... your creating more heat..increasing the crf. but it would need to increase by 200-300x what its current crf is now.. and it isnt going to do that only going 100 mph or whatever...
Guest
I have read the arguments with great interest. Here is my take. I have been a pilot for 25 years. The airplane will not fly!!!!!!!!!!! Here is why. There are forces that act on a plane, any plane or any object for that matter. They are trust, opposed by drag. And lift, opposed by gravity. The power source, what ever it may be, must overcome drag in order to move forward. Once it moves forward, enough lift must be acquired to over come gravity or the weight of the plane.

In several of the examples, ie bicycle on a treadmill or skateboarder or car, the one thing that was not changed was the speed of the treadmill once the force was applied to the object. Lets take the example of the bicycle. If you are holding the cycle while the treadmill runs and the wheels turn, you are applying a force equal to the amount of friction or drag on the wheels. If you where to let go, the bicycle would slowly go off the back of the treadmill because drag would now be greater than the force that was applied to hold it in position. (hold a car on a treadmill and then let go of the car and see what happens) If the speed of the treadmill were increased the wheels on the bicycle would spin faster and drag would increase because of friction and the amount of force needed to hold the bicycle in one place would have to be increased. If a greater force were applied to the bicycle, the treadmill would speed up, increase drag and negate the increase. You would never be able to push hard enough to make the bicycle move forward.

Assume the tires and wheel bearings on the plane have no limitations. The engines have a finite amount of trust. As the friction increases between the tires and the belt, more and more trust is needed. Once the drag or friction equaled the trust of the engines, the plane does not move forward. If the plane does not move forward due to the inability to overcome the constantly increasing drag the air does not flow over the wings and will not create the lift needed to overcome gravity and take off.

It's that simple.
sooks
and no jack.. i dotn think it can take off from stand still...thats idiotic.. it accellerates and continues too till take off because thrust is > than friction
Guest_3
Ok, there's a lot of people adding confusing stuff in here which really doesn't make any difference at all. The problem really needs to be simplified down to the only things that matter - the wheels, the conveyor, and the air that's providing the thrust.

So let's do an example with just those components to see if the plane will fly or not.

Say you've got one of those high-powered leaf-blowers that blows air out at a very fast speed. Now take a single wheel from say, a car or a plane, and put it on the ground.

Imagine your leaf-blower is actually big and powerful enough to blow the wheel forwards at a speed of 3mph on the ground. You could walk behind the wheel with the blower and the wheel would keep blowing along at a rate of 3mph as you walked. Right?

Now take the wheel and put it on the conveyor. Start the conveyor moving at 3mph (in either direction, it doesn't matter).

Now imagine standing on the conveyor behind the wheel with your leaf blower. At this point neither you nor the wheel would be physically moving on the belt, but you'd both be moving at 3mph in relation to the ground.

Now start up your leaf blower and point it at the wheel again. What happens?

Does the wheel move? And if so, at what speed are you walking at? Think about what's happening to the wheel being forced by the air. And what would be both yours and the wheel's speed in relation to the actual ground? The answer's very simple.

Now when you've got your answers to that, turn your wheel around on the conveyor so that you're now facing the opposite direction on the belt, and again use your leaf blower to blow on the wheel.

Again, what happens to the wheel?

If you can work out the answers to these simple questions, determining whether the plane will fly or not should be very easy indeed. There's no other factors to consider.

Guest
QUOTE (Guest_3+Feb 8 2006, 09:17 PM)
Ok, there's a lot of people adding confusing stuff in here which really doesn't make any difference at all. The problem really needs to be simplified down to the only things that matter - the wheels, the conveyor, and the air that's providing the thrust.

So let's do an example with just those components to see if the plane will fly or not.

Say you've got one of those high-powered leaf-blowers that blows air out at a very fast speed. Now take a single wheel from say, a car or a plane, and put it on the ground.

Imagine your leaf-blower is actually big and powerful enough to blow the wheel forwards at a speed of 3mph on the ground. You could walk behind the wheel with the blower and the wheel would keep blowing along at a rate of 3mph as you walked. Right?

Now take the wheel and put it on the conveyor. Start the conveyor moving at 3mph (in either direction, it doesn't matter).

Now imagine standing on the conveyor behind the wheel with your leaf blower. At this point neither you nor the wheel would be physically moving on the belt, but you'd both be moving at 3mph in relation to the ground.

Now start up your leaf blower and point it at the wheel again. What happens?

Does the wheel move? And if so, at what speed are you walking at? Think about what's happening to the wheel being forced by the air. And what would be both yours and the wheel's speed in relation to the actual ground? The answer's very simple.

Now when you've got your answers to that, turn your wheel around on the conveyor so that you're now facing the opposite direction on the belt, and again use your leaf blower to blow on the wheel.

Again, what happens to the wheel?

If you can work out the answers to these simple questions, determining whether the plane will fly or not should be very easy indeed. There's no other factors to consider.

Only when the force of the treadmill matches the force of the plane will the following occur:

Both the wheels and the tires will spin at the same speed.

The plane will appear 'stationary' over the ground.

The treadmill's belt thinks the plane is comming at it at 10mph closing speed.

The plane thinks it's going at 10mph closing speed over the TREADMILL.

The air molecules over the wing are not moving.

The plane dosn't fly.
Jack
Amen! Simplify, Simplify, Simplify.

I don't know who started talking about coefficients of friction in here...
sooks
QUOTE (Jack+Feb 8 2006, 09:26 PM)
Amen! Simplify, Simplify, Simplify.

I don't know who started talking about coefficients of friction in here...

its a physics board...thought youd be able to understand physics....guess not
Guest
I'm jumping in from another forum. No, I didn't read this whole thing, but I did read the one on my forum, and it rivals this one. Heh, I thought there would be more brainpower at work here, but I think I was mistaken.

All you guys who think that the belt can't hold the plane? What about friction? Talk about sheesh! Friction increases with speed. Belt can go infinitely fast. Friction goes up to whatever it needs to be to hold back the plane. Even King Kong and 100 jet engines don't have the power of infinity!

But how in the heck did a bunch of guys on a PHYSICS board, physics, a science that considers such singularities as black holes, for crying out loud, get to the point of anything moving, given the original question?

You can't divide by zero, any computer can tell you that.
sooks
because its not matching the speed of the wheels.. the wheels arent goign to infinity... only 2x the plane speed.. so friction isnt infinity... its very minor...
Guest
OK gentlemen, let's look at this a different way.

Let's replace the aircraft with an airboat - like what is used in the everglades.

Let's replace the conveyor with a smooth river, which is flowing from N to South, like the Mississippi. No chop.

The 'conundrum' we have, now, is this.

The airboat wishes to travel upstream. The V-8 engine attached to the PROP in the cage on the back of the boat is capable of moving the boat at 120 knots across the water (a smooth, motionless lake).

If we have a changing river current which magically can change from 0 to 120 knots to 'match' the speed of the boat. But its matching the speed of the boat compared to what? DEFINE THAT.

If the airboat starts at point A (as measured on the BANK of the river, with a NON-moving point of reference), and the river current then increases, will the boat ever be able to travel, say a few miles upstream. Or even a few feet? This is exactly like the aircraft conundrum, only with more easy-to-grasp principles.

This airboat does NOT use a prop inserted into the river to derive is propulsion by pushing against water. It depents entirely on the fan on the back of the boat. The speed of the boat is determined by its AIRSPEED. ALso, we will negate any viscosity of the river as the bottom of our boat is shaped very well and waxed.

So, with all things being considered, will the boat be able to make headway against a 60 mph current? Or a 120 mph current? Remember, the POINT OF REFERENCE is OFF THE RIVER.

????
sooks
this has been discussed several times... yes... it will go roughly the same speed no matter which way the current is going... (there is some minute friction..much like the plane) but still goes pretty much as normal
krreagan
QUOTE (Guest+Feb 8 2006, 01:36 PM)
When the rubber is warmed, it get's 'stickier', thus it's able to produce more friction. But when heat is added to a properly inflated tire, the air pressure will increase by a couple psi...making it produce a little less friction.

However, running an improperly inflated tire at high speed will cause too much heat, and the tire will come apart (remember the Firestones on Explorers?). Under normal circumstances they were fine...but if they were just a little underinflated, and a little overloaded, BOOM!

It's a point you refuse to accept. Tires freewheeling on the ground WILL generate heat. The faster you spin them, the more heat is generated. So, the faster you run that treadmill, the more friction you are creating, thus heating up those tires...where is that heat comming from? It's comming from it's efforts to slow the plane down!

Put a a fan on a skateboard, and put that onto a treadmill. Turn on the fan, and then turn on the treadmill...you WILL be able to achieve equilibrium, and the skateboard will appear to 'stand still'.

Go to a skatepark, and right after Tony Hawk gets off the ramp, see how hot those wheels are!!! Not in the bearings...the surface of the wheel...it's hot!!

The friction and the heat build higher and higher as speed increases.

This is the same garbage first spewed by Atl5p (if I'm not mistaken) I suspect these might be a cut-and-paste of some of those earlier posts. I recognize several of his ignorant arguments (and wording).

I suspect Atl5p has choked up some more of his illogical brain matter once again.

Krreagan
isfn
QUOTE (Guest+Feb 8 2006, 09:06 PM)
I have read the arguments with great interest. Here is my take. I have been a pilot for 25 years. The airplane will not fly!!!!!!!!!!! Here is why. There are forces that act on a plane, any plane or any object for that matter. They are trust, opposed by drag. And lift, opposed by gravity. The power source, what ever it may be, must overcome drag in order to move forward. Once it moves forward, enough lift must be acquired to over come gravity or the weight of the plane.

In several of the examples, ie bicycle on a treadmill or skateboarder or car, the one thing that was not changed was the speed of the treadmill once the force was applied to the object. Lets take the example of the bicycle. If you are holding the cycle while the treadmill runs and the wheels turn, you are applying a force equal to the amount of friction or drag on the wheels. If you where to let go, the bicycle would slowly go off the back of the treadmill because drag would now be greater than the force that was applied to hold it in position. (hold a car on a treadmill and then let go of the car and see what happens) If the speed of the treadmill were increased the wheels on the bicycle would spin faster and drag would increase because of friction and the amount of force needed to hold the bicycle in one place would have to be increased. If a greater force were applied to the bicycle, the treadmill would speed up, increase drag and negate the increase. You would never be able to push hard enough to make the bicycle move forward.

Assume the tires and wheel bearings on the plane have no limitations. The engines have a finite amount of trust. As the friction increases between the tires and the belt, more and more trust is needed. Once the drag or friction equaled the trust of the engines, the plane does not move forward. If the plane does not move forward due to the inability to overcome the constantly increasing drag the air does not flow over the wings and will not create the lift needed to overcome gravity and take off.

It's that simple.

The drag created by an itty bitty wheel is enough to overcome the thrust of an airplane engine?

If the wheels created that much drag then why isn't there a sudden burst of acceleration when the plane leaves the ground?

Since when can't you push a bike forward on a moving treadmill?
QUOTE (Guest+Feb 8 2006, 09:06 PM)
I have read the arguments with great interest. Here is my take. I have been a pilot for 25 years. The airplane will not fly!!!!!!!!!!!

<snip>

Assume the tires and wheel bearings on the plane have no limitations. The engines have a finite amount of trust. As the friction increases between the tires and the belt, more and more trust is needed. Once the drag or friction equaled the trust of the engines, the plane does not move forward. If the plane does not move forward due to the inability to overcome the constantly increasing drag the air does not flow over the wings and will not create the lift needed to overcome gravity and take off.

My father was a pilot with TWA for more than 30 years and his first reaction was "the plane can't fly". It took three email exchanges before he finally replied with "ARRrrrggh"... now I get it!"

You people who claim the plane can't fly are only responding with your gut reaction. Mine as well, was that the plane can't fly. After a lot of thought I realized how wrong I was... and you will too... eventually. That's what makes this problem so interesting.

Deconstructing the Airplane on a Conveyor Belt Problem
Hidden_Tiger
Since people are STILL confused I'll repeat my earlier post. The point of the riddle is that it's a trick question - it gets you to confuse a moving conveyor with a moving frame of reference:

QUOTE (darwin+Jan 15 2006, 05:27 PM)
The conveyor would not effect the atmospheric conditions created by the aircrafts propulsion unit(s) or minimally.

Right. Here's another way to look at it for those of you who are still confused (as was I at first):

Case 1: Car on treadmill - treadmill can prevent car from moving relative to ground
Case 2: Car with large fan attached to the ground behind it - fan cannot affect car (or will affect it minimally due to drag)
Case 3: Airplane with large fan attached to the ground behind it - if the fan blows air at the same speed the plane moves, then the plane will not be moving with respect to the air - fan can prevent airplane from moving
Case 4: Airplane on treadmill - treadmill cannot affect plane's movement, since all it can due is cause minimal friction on the wheels

The riddle expoits the fact that velocity addition between frames ONLY works when the relevant medium is moving. For example, if the entire world (AIR and all) were moving backwards at the speed of the plane, it would be true that from an outside the observer the plane would not be moving. However, we're only moving an insignificant part of the world (the treadmill) that doesn't affect the plane's motion.

It's a good riddle with a simple conclusion- don't make it more complicated than it is. Yes there's drag, but (as pointed out by isfn) the fact that planes take off smoothly shows that taking away the drag doesn't make a huge difference in the speed of the plane.
I don't think that being a pilot would help understand this question, unless you regularly take off on conveyor belts
To Those Who Think The Aiplane Will Remain Stationary

This situation is logically impossible, so stop saying that the plane won't move.

1) The original problem states that the belt matches the speed of the plane at all times.

2) If the plane is not moving, then the belt does not move.

3) If the belt doesn't move, it isn't acting on the plane IN ANY WAY with respect to forward motion.

What you are claiming in this circumstance is that the airplane is sitting on a non-moving surface with it's engines at full thrust... and not moving. This, in itself, is PROOF that the airplane moves. And if the airplane moves, then it is not stationary.
egnorant
As long as people measure belt speed against the ground and plane speed against the belt they will be confused.
Suppose that the belt moved in the same direction as the plane???
If it can move in the opposite direction, surely it can move in the same direction!
Would the plane take off any quicker?
Would the wheels spin at all?
It might takeoff a bit faster due to the now absent friction from the wheels.
Just as in the stated problem it will take off with a little additional friction.

The "no fly" guys have the plane POINTED in a direction, but they never let it move!
The only thing moving in the "no fly" camp is the belt.
This violates the wording of the puzzle!
Bruce
B_bowler
QUOTE (egnorant+Feb 9 2006, 06:53 AM)
Suppose that the belt moved in the same direction as the plane???
If it can move in the opposite direction, surely it can move in the same direction!
Would the plane take off any quicker?

No it would not take off any faster, but it would need much less runway (belt) than on normal ground.

As far as speed goes it's airspeed would still be the same as normal, as would be the amount of thrust required by the plane. This is exactly what happens when planes take off on aircraft carriers.

The speed of the plane, in addition to the speed provided by the ship, makes it much easier for the plane to attain the airspeed it needs in order to get airborne. And the net result is the plane requires a much shorter runway to take off.

If the plane needs to be travelling at an airspeed of 80 knots to lift off, on a ship that's travelling forwards at 40 knots it would need (roughly) half the amount of runway to take off that it would need on a regular runway. The runway length is greatly reduced.

Of course, the plane would still need to be exerting the same amount of thrust it normally needs to fly, because once it takes off it would not remain airborne very long without it.

Now imagine what would happen if the ship was travelling at 80 knots. The plane would not need any runway to take off at all. It would simply lift up into the air due to the airflow over it's wings being provided by the ship.

But again, he would still need to be thrusting just the same as he normally would, in order to remain airborne once he gets up.

So the ships's speed greatly influences the amount of runway needed to take off.

So now imagine what happens if the ship is actually going backwards instead of forwards. This increases the amount of runway the plane would normally need to take off.

Going forwards it can reduce the runway needed right down to zero. Going in the oppposite direction it can increase it right up to infinity (i.e. the plane would not take off).

Taking the example from above:

Ship's speed Runway needed
=========================

0------------------------Same as on regular ground

40-----------------------Half what is normally required

80-----------------------None at all

-40----------------------Double what is normally required

-80----------------------Goes to infinity

If the plane going forwards is matched by the ship going backwards it would need an infinite amount of runway to get up to the airspeed it needs to take off.

Guest
Hi guys, I've been following this discussion for some time and I have to say I entirely agree with the no-flyers - the plane won't fly!!

This is such BASIC physics but I can see a lot of you are going to take some convincing...

OK, look at it like this.

Say you've got a toy boat, and the boat's maximum speed is 10mph. Put the boat on a perfectly calm lake, and it whizzes around at 10mph. I think you'll also agree that the air is also flowing over the boat at 10mph. Right?

Now take the boat and find a river which is flowing *downstream* at 10mph. If you put the boat on the river facing in the opposite direction, how far does it move? It does not move at all. In fact, it's sitting *perfectly still* on the water. The forwards thrust of the boat is completely negated by the force of the river.

So how much air is flowing over the boat now?? None!!! It's stationary. The river might be moving, but the *air around the boat* is not moving at all! And this is what the problem is: the boat needs to be moving in relation to the *air around it* - NOT in relation to the river!!

Now put some wings on the boat. Increase the speed of the river by 10mph, and the speed of the boat-plane by the 10mph. How fast is it moving now?? It's still not moving!! If you were a person standing on the river bank watching this fiasco, the plane would still be sitting right in front of you, it would not have budged an inch. Even though it's now applying 20mph of *thrust*, the actual airspeed of the plane is still zero! And airspeed is what you need for a plane to fly...

In fact you'd even be able to walk up to the plane and feel with your own hands that there was NO air flowing over the wings WHATSOEVER!!

In order for this boat-plane to be able to take off, it would actually need to be travelling at 200% the speed of *whatever* the river is travelling at in order to get airborne. But since, in this example, the speed of the river (or the conveyor belt) *always* matches whatever the boat-plane is doing, your speed will never be more than 100%, it would never be able to move forwards from it's starting position, and the air would never flow over it.

It would not stand a chance in hell of taking off!

Have a nice day!
sooks
QUOTE (Guest+Feb 9 2006, 01:31 PM)
Hi guys, I've been following this discussion for some time and I have to say I entirely agree with the no-flyers - the plane won't fly!!

This is such BASIC physics but I can see a lot of you are going to take some convincing...

OK, look at it like this.

Say you've got a toy boat, and the boat's maximum speed is 10mph. Put the boat on a perfectly calm lake, and it whizzes around at 10mph. I think you'll also agree that the air is also flowing over the boat at 10mph. Right?

Now take the boat and find a river which is flowing *downstream* at 10mph. If you put the boat on the river facing in the opposite direction, how far does it move? It does not move at all. In fact, it's sitting *perfectly still* on the water. The forwards thrust of the boat is completely negated by the force of the river.

So how much air is flowing over the boat now?? None!!! It's stationary. The river might be moving, but the *air around the boat* is not moving at all! And this is what the problem is: the boat needs to be moving in relation to the *air around it* - NOT in relation to the river!!

Now put some wings on the boat. Increase the speed of the river by 10mph, and the speed of the boat-plane by the 10mph. How fast is it moving now?? It's still not moving!! If you were a person standing on the river bank watching this fiasco, the plane would still be sitting right in front of you, it would not have budged an inch. Even though it's now applying 20mph of *thrust*, the actual airspeed of the plane is still zero! And airspeed is what you need for a plane to fly...

In fact you'd even be able to walk up to the plane and feel with your own hands that there was NO air flowing over the wings WHATSOEVER!!

In order for this boat-plane to be able to take off, it would actually need to be travelling at 200% the speed of *whatever* the river is travelling at in order to get airborne. But since, in this example, the speed of the river (or the conveyor belt) *always* matches whatever the boat-plane is doing, your speed will never be more than 100%, it would never be able to move forwards from it's starting position, and the air would never flow over it.

It would not stand a chance in hell of taking off!

Have a nice day!

man... how many times have you guys tried this argument.. Sir, your wrong. Well your right, the boat will be stationary. However, the boat is propelled from a prop in the water and pushes the water to move forward. If you have a flow of water going against the prop.... its the same as a car on the treadmill... it takes away from it.

Now, if we change the boat to a fan boat...ya know like you see in the everglades and what not. where everything is above the water. That boat pushes the air and will still be able to cruise 10 mph no matter what the river is doing minus a little bit of friction from the drag in water. it cruises on the surface of the water and not in it like a boat. this is like a plane on top of a conveyor belt.
Guest
QUOTE (sooks+Feb 9 2006, 03:20 PM)

man... how many times have you guys tried this argument.. Sir, your wrong. Well your right, the boat will be stationary. However, the boat is propelled from a prop in the water and pushes the water to move forward. If you have a flow of water going against the prop.... its the same as a car on the treadmill... it takes away from it.

Now, if we change the boat to a fan boat...ya know like you see in the everglades and what not. where everything is above the water. That boat pushes the air and will still be able to cruise 10 mph no matter what the river is doing minus a little bit of friction from the drag in water. it cruises on the surface of the water and not in it like a boat. this is like a plane on top of a conveyor belt.

Yes, a fan boat can move on the water at 10mph...and if the water underneath the boat is moving in the opposite direction at 10mph, that means that IF THE BOAT WERE ON LAND AND HAD WHEELS, the same engine setting would propel that boat 20mph!!!
Guest_bowler
QUOTE (sooks+Feb 9 2006, 03:20 PM)
man... how many times have you guys tried this argument..  Sir, your wrong.  Well your right, the boat will be stationary.  However, the boat is propelled from a prop in the water and pushes the water to move forward.  If you have a flow of water going against the prop.... its the same as a car on the treadmill... it takes away from it.

Now, if we change the boat to a fan boat...ya know like you see in the everglades and what not.  where everything is above the water.  That boat pushes the air and will still be able to cruise 10 mph no matter what the river is doing minus a little bit of friction from the drag in water.  it cruises on the surface of the water and not in it like a boat.  this is like a plane on top of a conveyor belt.

No, he's actually right on this.

The boat is still affected by the flow of the river regardless of which method of propulsion it's using.

Imagine you've got a normal boat with a prop sitting on the river, and the river's flowing at a steady 5mph. What's making the boat flow downstream with the river? It's the water's current acting on the aerodynamics of the body of the boat, creating drag, and causing the boat to flow downstream right?

Now imagine taking the prop and outboard motor off the back of the boat and replacing it with a fan. What's changed to the boat's movement on the water? Nothing. It's still going downstream at 5mph just as before.

Putting a fan on a boat does not change the shape of the boat, the amount of water it displaces, the aerodynamics, or the amount of drag created on it by the water. Putting a fan on the back does not make the boat 'float on the water' like you say, it's still sitting in the water just like it was when the boat had a prop.

It doesn't suddenly become unaffected by the flow of the river!

The only vehicle that can do this is a hovercraft, because it's sitting above the surface of the water! All other boats are sitting in the water, not on it!
Hidden_Tiger
QUOTE (Guest_bowler+Feb 9 2006, 04:51 PM)
Imagine you've got a normal boat with a prop sitting on the river, and the river's flowing at a steady 5mph. What's making the boat flow downstream with the river? It's the water's current acting on the aerodynamics of the body of the boat, creating drag, and causing the boat to flow downstream right?

No, it's not - once the boat is moving at a reasonable clip, the drag force of the water is not playing a major role. The main problem is that the boat's prop is trying to push against something that's MOVING. The fan doesn't have this problem.

Imagine that you're trying to climb a ladder. If the ladder is moving down at 5 mph, you will need to climb up at 5 mph just to stay in the same spot. Now strap on a jet engine. While it's true that the ladder will be smacking against your hands and feet as you cruise upwards, this drag force doesn't make a huge difference (besides being painful). Therefore the speed of the ladder doesn't subtract away your speed.
Hidden_Tiger
Since this is a physics forum, I decided to do some physics to prove the "it will fly" theory. I'll use only basic mechanics and some very basic calculus:

There are two forces acting on the plane - the force from the engines (F) and a frictional force from the conveyor belt (f). The belt and plane have the same acceleration (a), since the problem says that the belt matches the speed of the plane. For the purpose of clarity I've assumed that the plane only has one wheel, but the proof for multiple wheels would be virtually identical. Given the mass of the plane (M), mass of the wheel (m), and the radius of the wheel ® I can write a force-balance equation and a torque-balance equation:

(M+m)*a = F - f
f*r = 1/2*m*r^2*k
where k is the angular acceleration (sorry, can't figure out how to get an alpha symbol on here) and I assume the wheel is a cylinder (thus giving it a moment of inertia of 1/2*m*r^2)

How does k relate to a? Well, we know that the distance traveled by the plane since the beginning (t=0) will be equal to the distance traveled by the wheels minus the distance traveled by the conveyor belt:
dist(plane) = dist(wheels) - dist(belt)
d = r*(theta - 1/2*a*t^2
v = r*(angular velocity) - a*t (differentiating once)
a = r*k - a (differentiating again)
so k = 2a/r

Plugging back into our first equation, F = (M+m)*a + f = (M+m)*a + 1/2*m*r*k = (M+m)*a + m*a

So, we see that F = (M+2m)a, meaning that the external force applied by the engines will need to be greater only by a factor of m*a, which is negligible for M>>m (which is the case for any airplane)

Many of the arguments made by other posters are confirmed by these calculations. For example, kr = 2a, meaning that the wheels are accelerating angularly at twice their normal speed.
Another important point that comes out this - there is a relationship between the magnitude of the frictional force and the rotation of the wheel. Therefore the frictional force can't "go to infinity" as some have suggested. Since the plane is not slipping on the conveyor belt, the rotation of the wheels, the speed of the plane, the velocity of the belt, and the frictional force are all dependent on one another. Notice that in the proof above I did not set a limit on the frictional force (a coefficient of friction, etc.) - I showed that the frictional force MUST be m*a to preserve the motion of the plane
I've assumed that there is no "rolling friction" - that is, friction that does not spin the wheels (i.e. a sticky surface). Even if there were, it would not change the analysis - since this friction often modeled as linearly proportional to wheel velocity (which is twice as fast with a conveyor belt), we would have F = (M+m)a + f(rolling) jump to F = (M+2m)a + 2*f(rolling), which is still only a jump of ma+f(rolling). This is not a big deal to a plane, since air resistance is much larger than rolling friction anyway (air resistance is proportional to v^2).

Note also that these equations would not apply to a car since an external force F is required, which in this case is provided by the engines. For a car, the frictional force is USED to accelerate the car (which is why a car is useless on ice). In this case k = 2a/r as above, and it is still true that f = ma. Our equation of motion is, however,(M+m)a = f (note that there is no F in the equation as with the plane). This gives (M+m)a=ma. Subtracting ma, we find that Ma = 0. Since M is not equal to zero, this means that a = 0 so these same equations predict that the car does not move while the airplane does.

When it comes down to it, equations have precedence over intuition. Luckily the equations agree with the major intuition on this board, so they only support each other.
Finally! Thank you, Hidden_Tiger.

Can I get your permission to use your analysis on my website?
Guest
QUOTE (Hidden_Tiger+Feb 9 2006, 08:04 PM)
Since this is a physics forum, I decided to do some physics to prove the "it will fly" theory. I'll use only basic mechanics and some very basic calculus:

There are two forces acting on the plane - the force from the engines (F) and a frictional force from the conveyor belt (f). The belt and plane have the same acceleration (a), since the problem says that the belt matches the speed of the plane. For the purpose of clarity I've assumed that the plane only has one wheel, but the proof for multiple wheels would be virtually identical. Given the mass of the plane (M), mass of the wheel (m), and the radius of the wheel ® I can write a force-balance equation and a torque-balance equation:

(M+m)*a = F - f
f*r = 1/2*m*r^2*k
where k is the angular acceleration (sorry, can't figure out how to get an alpha symbol on here) and I assume the wheel is a cylinder (thus giving it a moment of inertia of 1/2*m*r^2)

How does k relate to a? Well, we know that the distance traveled by the plane since the beginning (t=0) will be equal to the distance traveled by the wheels minus the distance traveled by the conveyor belt:
dist(plane) = dist(wheels) - dist(belt)
d = r*(theta - 1/2*a*t^2
v = r*(angular velocity) - a*t (differentiating once)
a = r*k - a (differentiating again)
so k = 2a/r

Plugging back into our first equation, F = (M+m)*a + f = (M+m)*a + 1/2*m*r*k = (M+m)*a + m*a

So, we see that F = (M+2m)a, meaning that the external force applied by the engines will need to be greater only by a factor of m*a, which is negligible for M>>m (which is the case for any airplane)

Many of the arguments made by other posters are confirmed by these calculations. For example, kr = 2a, meaning that the wheels are accelerating angularly at twice their normal speed.
Another important point that comes out this - there is a relationship between the magnitude of the frictional force and the rotation of the wheel. Therefore the frictional force can't "go to infinity" as some have suggested. Since the plane is not slipping on the conveyor belt, the rotation of the wheels, the speed of the plane, the velocity of the belt, and the frictional force are all dependent on one another. Notice that in the proof above I did not set a limit on the frictional force (a coefficient of friction, etc.) - I showed that the frictional force MUST be m*a to preserve the motion of the plane
I've assumed that there is no "rolling friction" - that is, friction that does not spin the wheels (i.e. a sticky surface). Even if there were, it would not change the analysis - since this friction often modeled as linearly proportional to wheel velocity (which is twice as fast with a conveyor belt), we would have F = (M+m)a + f(rolling) jump to F = (M+2m)a + 2*f(rolling), which is still only a jump of ma+f(rolling). This is not a big deal to a plane, since air resistance is much larger than rolling friction anyway (air resistance is proportional to v^2).

Note also that these equations would not apply to a car since an external force F is required, which in this case is provided by the engines. For a car, the frictional force is USED to accelerate the car (which is why a car is useless on ice). In this case k = 2a/r as above, and it is still true that f = ma. Our equation of motion is, however,(M+m)a = f (note that there is no F in the equation as with the plane). This gives (M+m)a=ma. Subtracting ma, we find that Ma = 0. Since M is not equal to zero, this means that a = 0 so these same equations predict that the car does not move while the airplane does.

When it comes down to it, equations have precedence over intuition. Luckily the equations agree with the major intuition on this board, so they only support each other.

Why doesn't the car move? It will just rotate its wheels at twice the rate in the acceleration process. I know it won't fly, but it should get up to any speed within its power range.
QUOTE (Guest+Feb 9 2006, 09:34 PM)
Why doesn't the car move? It will just rotate its wheels at twice the rate in the acceleration process. I know it won't fly, but it should get up to any speed within its power range.

Holy carp, you are right.

For some reason, I was assuming that a car on the belt wouldn't move, but that violates my argument of creating an illogical situation. If the car doesn't move then the belt doesn't move, as per the wording of the original question.

A car on the belt *will* move if only because the belt only moves when it detects a non-zero velocity of the car with respect to the ground.
Atl5p
QUOTE (sooks+Feb 9 2006, 10:20 AM)
QUOTE (Guest+Feb 9 2006, 01:31 PM)
Hi guys, I've been following this discussion for some time and I have to say I entirely agree with the no-flyers - the plane won't fly!!

This is such BASIC physics but I can see a lot of you are going to take some convincing...

OK, look at it like this.

Say you've got a toy boat, and the boat's maximum speed is 10mph. Put the boat on a perfectly calm lake, and it whizzes around at 10mph. I think you'll also agree that the air is also flowing over the boat at 10mph. Right?

Now take the boat and find a river which is flowing *downstream* at 10mph. If you put the boat on the river facing in the opposite direction, how far does it move? It does not move at all. In fact, it's sitting *perfectly still* on the water. The forwards thrust of the boat is completely negated by the force of the river.

So how much air is flowing over the boat now?? None!!! It's stationary. The river might be moving, but the *air around the boat* is not moving at all! And this is what the problem is: the boat needs to be moving in relation to the *air around it* - NOT in relation to the river!!

Now put some wings on the boat. Increase the speed of the river by 10mph, and the speed of the boat-plane by the 10mph. How fast is it moving now?? It's still not moving!! If you were a person standing on the river bank watching this fiasco, the plane would still be sitting right in front of you, it would not have budged an inch. Even though it's now applying 20mph of *thrust*, the actual airspeed of the plane is still zero! And airspeed is what you need for a plane to fly...

In fact you'd even be able to walk up to the plane and feel with your own hands that there was NO air flowing over the wings WHATSOEVER!!

In order for this boat-plane to be able to take off, it would actually need to be travelling at 200% the speed of *whatever* the river is travelling at in order to get airborne. But since, in this example, the speed of the river (or the conveyor belt) *always* matches whatever the boat-plane is doing, your speed will never be more than 100%, it would never be able to move forwards from it's starting position, and the air would never flow over it.

It would not stand a chance in hell of taking off!

Have a nice day!

man... how many times have you guys tried this argument.. Sir, your wrong. Well your right, the boat will be stationary. However, the boat is propelled from a prop in the water and pushes the water to move forward. If you have a flow of water going against the prop.... its the same as a car on the treadmill... it takes away from it.

Now, if we change the boat to a fan boat...ya know like you see in the everglades and what not. where everything is above the water. That boat pushes the air and will still be able to cruise 10 mph no matter what the river is doing minus a little bit of friction from the drag in water. it cruises on the surface of the water and not in it like a boat. this is like a plane on top of a conveyor belt.

That's really stupid soocks

Try a sail boat.

It can move at 15mph through the water.

But go to the Florida Straights and sail Westbound against the Gulf Stream Current at 6mph in the opposite direction.

How fast do you think you'd go over the bottom of the ocean?

15mph - 6mph = 9mph 'ground speed'.

You're ignorant. And I've actually done that BTW.

Except our knot meter read only 9 knts. And our chart said the current was moving opposite us at 6 kts. Yeah, we were only moving at 3knts 'reletive to the earth'.

Last I checked, a sailboat is powered by the WIND. (and you ARE ignorant)

So are you REALLY saying that a Sailboat is not affected in the LEAST by the currents of the ocean??? Damn....go back to kinderkare.
Atl5p
QUOTE (Hidden_Tiger+Feb 9 2006, 12:48 PM)
QUOTE (Guest_bowler+Feb 9 2006, 04:51 PM)
Imagine you've got a normal boat with a prop sitting on the river, and the river's flowing at a steady 5mph. What's making the boat flow downstream with the river? It's the water's current acting on the aerodynamics of the body of the boat, creating drag, and causing the boat to flow downstream right?

No, it's not - once the boat is moving at a reasonable clip, the drag force of the water is not playing a major role. The main problem is that the boat's prop is trying to push against something that's MOVING. The fan doesn't have this problem.

Imagine that you're trying to climb a ladder. If the ladder is moving down at 5 mph, you will need to climb up at 5 mph just to stay in the same spot. Now strap on a jet engine. While it's true that the ladder will be smacking against your hands and feet as you cruise upwards, this drag force doesn't make a huge difference (besides being painful). Therefore the speed of the ladder doesn't subtract away your speed.

dip s..... oh, why bother.....

See, you forgot to put a matching jet engine onto the ladder.

Sure you can ALWAYS overpower the ladder...but then you wouldn't be 'matching speeds'.
Atl5p
QUOTE (krreagan+Feb 8 2006, 02:57 PM)
QUOTE (Guest+Feb 8 2006, 11:35 AM)
I believe I DO understand the question....there are just many folks out here that don't have much common sence.

The prop is not causing the air to travel over the wings...the prop is just pulling a 'cylinder' of air...displacing it from 'in front' of the plane to 'the back' of the plane.

That force causes an equal and opposite action on the rest of the plane, causing it to move forward in relation to the ground it is sitting on.

When the plane is at rest, the only other force acting on the plane is gravity, which is 'sticking' the plane to the ground.  If the ground is 'stationary', then the plane moves forward through the air.  Conversly, if the ground is 'moving backwards' as in a tread mill, all forward motion reletive to the tower is negated.  Thus no air moves across the wings, thus there is NO LIFT.

I understand where the 'It will Fly' people are going wrong...they are assuming that all the air is physically connected.  If you pull the cylinder of air via the prop, then you believe that 'all the air around the plane' will start to move as well....this is backwards.

What is really happening is the prop is moving a horizontal column of air...normally that causes the plane to move in relation to the ground...it's THIS movement that causes the calm air surrounding the ground to become attacked by the wing.

However, when the 'ground' is moving backwards, all forward momentum is stopped, thus no lift.

You may understand the question, you just don't appear to know how to apply the physical concepts to arrive at an acceptable solution!!

The plane generates thrust (force) to move forward. The belt moves in the opposite direction but applies virtually no force on the plane!

1} What force is being used to counter the force from the planes engines?

2} How is this force transfered from the belt to the plane?

Answer both of these and you will have converts! (Hint: Nobody in 270+ pages has been able to do it acceptably!).

Krreagan

So, what you're saying is that a sailboat (powered by wind) is not at all affected by the ocean's currents?

You need to speak to Christopher Columbus, "dipshit".

The same boat....it has an aux engine. The engine can make it go 10mph. Or The wind can make it go 10mph. So, when you are in an opposing current of say 10mph, what you are saying is that

"it's best to cut the engine and raise the sails"--Kreegan

...because once you do that, the ocean's current will have no effect on the boat any longer?

Try it with an ocean-going sailboat with a 7ft draft.

Now try it with a day-sailer that has a 2' daggerboard.

The ocean current will affect the boat the same, regardless of the source of propulsion, prop or sail....the 'effing GPS tells me so....the knotmeter tells me so....get off my boat Kreegan before we hit a reef!!!

The treadbelt will affect the car/plane, regardless of the source of propulsion. (same as above)...

In so many ways, Kreegan, you are so wrong.....everything is wrong....this whole 'airboat' vs 'propboat' is a dream...

Hidden_Tiger
QUOTE (Skadar+Feb 9 2006, 10:01 PM)
QUOTE (Guest+Feb 9 2006, 09:34 PM)
Why doesn't the car move?  It will just rotate its wheels at twice the rate in the acceleration process.  I know it won't fly, but it should get up to any speed within its power range.

Holy carp, you are right.

For some reason, I was assuming that a car on the belt wouldn't move, but that violates my argument of creating an illogical situation. If the car doesn't move then the belt doesn't move, as per the wording of the original question.

A car on the belt *will* move if only because the belt only moves when it detects a non-zero velocity of the car with respect to the ground.

PLEASE READ!! I think I've found an answer that we can all agree on!! (Even the boaters - take a look at the end of the post)

You guys are right, I made a mistake in my original analysis. The car WILL be able to move on the treadmill, it will just have a slower acceleration than normal. I had forgotten to add in the car's engine torque to the equation.
Looks like the solution is much more difficult than I had thought! I apologize to the other people about the boat/car analogies, I was wrong. But the conclusion is still the same - the plane flies!

Here are the equations again, with a corrected car section at the bottom. And Skadar, I would have no problem if you posted these elsewhere:

There are two forces acting on the plane - the force from the engines (F) and a frictional force from the conveyor belt (f). The belt and plane have the same acceleration (a), since the problem says that the belt matches the speed of the plane. For the purpose of clarity I've assumed that the plane only has one wheel, but the proof for multiple wheels would be virtually identical. Given the mass of the plane (M), mass of the wheel (m), and the radius of the wheel ® I can write a force-balance equation and a torque-balance equation:

(M+m)*a = F - f
f*r = 1/2*m*r^2*k
where k is the angular acceleration and I assume the wheel is a cylinder (thus giving it a moment of inertia of 1/2*m*r^2)

How does k relate to a? Well, we know that the distance traveled by the plane since the beginning (t=0) will be equal to the distance traveled by the wheels minus the distance traveled by the conveyor belt:
dist(plane) = dist(wheels) - dist(belt)
d = r*(theta) - 1/2*a*t^2
v = r*(angular velocity) - a*t (differentiating once)
a = r*k - a (differentiating again)
so k = 2a/r

Plugging back into our first equation, F = (M+m)*a + f = (M+m)*a + 1/2*m*r*k = (M+m)*a + m*a

So, we see that the external force applied by the engines will need to be greater only by a factor of m*a, which is negligible for M>>m (which is the case for any airplane)

Many of the arguments made by other posters are confirmed by these calculations. For example, kr = 2a, meaning that the wheels are accelerating angularly at twice their normal speed.
Another important point that comes out this - there is a relationship between the magnitude of the frictional force and the rotation of the wheel. Therefore the frictional force can't "go to infinity" as some have suggested. Since the plane is not slipping on the conveyor belt, the rotation of the wheels, the speed of the plane, the velocity of the belt, and the frictional force are all dependent on one another. Notice that in the proof above I did not set a limit on the frictional force (a coefficient of friction, etc.) - I showed that the frictional force MUST be m*a to preserve the motion of the plane
I've assumed that there is no "rolling friction" - that is, friction that does not spin the wheels (i.e. a sticky surface). Even if there were, it would not change the analysis - since this friction often modeled as linearly proportional to wheel velocity (which is twice as fast with a conveyor belt), we would have F = (M+m)a + f(rolling) jump to F = (M+2m)a + 2*f(rolling), which is still only a jump of ma+f(rolling). This is not a big deal to a plane, since air resistance is much larger than rolling friction anyway (air resistance is proportional to v^2).

Note also that these equations would not apply to a car since an external force F is required, which in this case is provided by the engines. For a car, the frictional force is USED to accelerate the car (which is why a car is useless on ice). In this case:
Force Balance: (M+m)a = f
Torque Balance: T - f*r = 1/2*m*r^2*k (where T is the engine torque)
k = 2a/r as above
T - f*r = r*a*m
f = T/r - a*m
(M+m)a = T/r - a*m
a = (T/r)/(M+2m)

Without the treadmill, k = a/r and a = (T/r)/(M+3/2*m). Since the treadmill increases the denominator of the acceleration, it decreases the car's acceleration. IMPORTANT POINT! If we re-arrange the equation for the airplane, we get a = F/(M+2m). Since T/r is analogous to F, there is no difference between the airplane and the car!!! As per the wording of the original question, BOTH will accelerate at the same rate that the belt accelerates backwards. Each will require extra force/torque compared to stationary ground, but this extra force/torque is only on the order of m (the wheel mass) so it will not overcome the plane/car

Note that these equations do NOT apply to boats. These assume that the vehicle is moving along on wheels, which rotate and do not slip against the ground. This is definately NOT the case for boats. Although I don't have the equations to back this up, I would venture a guess that velocities simply add in the water - the velocity of the boat adds to the velocity of the current. Therefore you could never set up this "plane" experiment in the water, since having the current speed equal the boat speed would not allow the boat to move.
krreagan
QUOTE (Atl5p+Feb 9 2006, 07:29 PM)
QUOTE (krreagan+Feb 8 2006, 02:57 PM)
QUOTE (Guest+Feb 8 2006, 11:35 AM)
I believe I DO understand the question....there are just many folks out here that don't have much common sence.

The prop is not causing the air to travel over the wings...the prop is just pulling a 'cylinder' of air...displacing it from 'in front' of the plane to 'the back' of the plane.

That force causes an equal and opposite action on the rest of the plane, causing it to move forward in relation to the ground it is sitting on.

When the plane is at rest, the only other force acting on the plane is gravity, which is 'sticking' the plane to the ground.  If the ground is 'stationary', then the plane moves forward through the air.  Conversly, if the ground is 'moving backwards' as in a tread mill, all forward motion reletive to the tower is negated.  Thus no air moves across the wings, thus there is NO LIFT.

I understand where the 'It will Fly' people are going wrong...they are assuming that all the air is physically connected.  If you pull the cylinder of air via the prop, then you believe that 'all the air around the plane' will start to move as well....this is backwards.

What is really happening is the prop is moving a horizontal column of air...normally that causes the plane to move in relation to the ground...it's THIS movement that causes the calm air surrounding the ground to become attacked by the wing.

However, when the 'ground' is moving backwards, all forward momentum is stopped, thus no lift.

You may understand the question, you just don't appear to know how to apply the physical concepts to arrive at an acceptable solution!!

The plane generates thrust (force) to move forward. The belt moves in the opposite direction but applies virtually no force on the plane!

1} What force is being used to counter the force from the planes engines?

2} How is this force transfered from the belt to the plane?

Answer both of these and you will have converts! (Hint: Nobody in 270+ pages has been able to do it acceptably!).

Krreagan

So, what you're saying is that a sailboat (powered by wind) is not at all affected by the ocean's currents?

You need to speak to Christopher Columbus, "dipshit".

The same boat....it has an aux engine. The engine can make it go 10mph. Or The wind can make it go 10mph. So, when you are in an opposing current of say 10mph, what you are saying is that

"it's best to cut the engine and raise the sails"--Kreegan

...because once you do that, the ocean's current will have no effect on the boat any longer?

Try it with an ocean-going sailboat with a 7ft draft.

Now try it with a day-sailer that has a 2' daggerboard.

The ocean current will affect the boat the same, regardless of the source of propulsion, prop or sail....the 'effing GPS tells me so....the knotmeter tells me so....get off my boat Kreegan before we hit a reef!!!

The treadbelt will affect the car/plane, regardless of the source of propulsion. (same as above)...

In so many ways, Kreegan, you are so wrong.....everything is wrong....this whole 'airboat' vs 'propboat' is a dream...

Are you really still trying to fight this fight Atl5p?! Stubborn ignorance at its worst!

Your lack of critical thinking skills and ignorance of basic physical concepts is extremely well documented by your own posts on this list for all to see! So I will not bother repeating what has been stated many times in the past concerning the level of your ignorance of physical concepts.

I can excuse you lack of knowledge as not everyone has a science education, What I fault you for is your continued pushing of concepts that have been shown many many times, by many individuals, to be fatally flawed (not to mention ludicrous)! It has been explained to you in great detail and yet you refuse to accept it and cannot, or are unable to put forward a convincing argument!

I actually thought you had finally realized the errors of your ways! I guess not!

Krreagan
Hidden_Tiger
QUOTE (krreagan+Feb 10 2006, 06:45 AM)
QUOTE (Atl5p+Feb 9 2006, 07:29 PM)
In so many ways, Kreegan, you are so wrong.....everything is wrong....this whole 'airboat' vs 'propboat' is a dream...

Are you really still trying to fight this fight Atl5p?! Stubborn ignorance at its worst!

I think at Atl5p is actually right with respect to the boats. In the water, velocities just do a straight vector addition, regardless of power source. However, frictional forces acting on wheels (of a car/plane) are in no way analogous to those acting on a boat, so Atl5p is wrong to use this analogy to prove anything about the plane senario.
Guest

Hidden Tiger :
"you could never set up this "plane" experiment in the water, since having the current speed equal the boat speed would not allow the boat to move."

Regardless of the current(within reason), the boat WILL move forward...just that the frictional factors would be greater. Using a controled current as the "conveyor", a boat without wings will simply reach its maximum "water prop" speed as the current matches that speed. With wings, the boat will lift off and fly given ample air thrust in the design.
Fynlcut
Atl5P is wrong all the way around.
Airboat, and regualr boat in a river. Same thing as a plane and a car on a conveyor. The moving surface of the water will add more friction, it will noticably slow the forward progress of the airboat, but the boat will still move up stream.

Look at float planes. They will take off into the wind, as opposed to with or against the current. (Most of the time, occasionally there is some kook taking off from some fast river where it works out that down stream is always better than up.)
krreagan
QUOTE (Atl5p+Feb 9 2006, 07:29 PM)
....get off my boat Kreegan before we hit a reef!!!

No worries, I would never, ever get on/in a motorized vehicle that you were driving/piloting!

Krreagan
detatched
There once was a plane on conveyer
with many a yea and naysayer
they bellowed and raged for many a page,
for so long that their hair got much grayer.

GIVE IT UP PEOPLE!!!
bret f
QUOTE (Fynlcut+Feb 10 2006, 04:49 PM)
Atl5P is wrong all the way around.
Airboat, and regualr boat in a river. Same thing as a plane and a car on a conveyor. The moving surface of the water will add more friction, it will noticably slow the forward progress of the airboat, but the boat will still move up stream.

No dude, he's right. I've done this myself. Powerboat, fanboat, or sailboat, they're all affected by the current exactly the same, regardless of where the source is from.

If you're sailing with a tailwind against an equal current in the opposite direction then in relation to land you're not going anywhere at all. It looks pretty weird cos your sail's full of air and you know you must be going somewhere, but when you look at the land you're simply not going forwards.

In order to actually move forwards in relation to the land you'd need to be either sailing against a weaker current or to have more wind in your sails. If both forces are equal then you're never going anyhere.

Hell, if the current's stronger than the wind it's quite possible for you to be travelling backwards in relation to land! That does happen sometimes. That's just the way it works.

But if you don't believe me just jump in a sailboat yourself some time and you'll see how important the tides and currents are to your craft. Whether you're in a wind-powered or a motor-powered boat all current and tidal forces affect you, just the same.

Guest
Hey guys, just visiting here......

An interesting debate over the past 277 pages to be sure, and I would like to add to it, but just once!!

Since this is a allegedly a physics forum, let's use some physics!!!:

From Newton's 2nd law: E(sigma) F=ma

or the EFx+y (vector sum of all external forces acting on an object)=mass(*)acceleration.

In our example there are two opposing forces (we shall ignore lift and weight since it seems we all agree that with the proper airspeed, the plane will fly)

These forces are the thrust of the engines (x)and the friction of the wheel system (y) as it interacts with the moving conveyor system.

Friction is represented byFy= fk=ukn where uk is the coefficient of kinetic friction, which for steel on steel ball bearings is .17, and that is not allowing for the friction reducing effects of synthetic grease on the ball bearings.

Thrust is represented byFx= F=ma where m=the mass of air being processed through the engines, and a=the acceleration of that mass due to the burning of the jet fuel, increases in temperature and volume of the air, and the vector effects of the nozzle and fan design.

If Fx=Fy the combined but independent systems are at equilibrium and the plane has zero airspeed regardless of wheel speed. If Fx>Fy then a will be positive assuming m stays constant, generating positive acceleration, airspeed, and liftoff. If Fx<Fy then the engines will produce thrust, but will not be able to overcome the Fy and the plane will have zero airspeed and zero wheel speed. Sum the forces and you have your answer. Its not really that important if the airplane will fly or not, what is important is our understanding of the physics leading to the correct answer to the question: Why?

It is important to note that we are dealing with two iindependent systems here, the atmospheric system and its relation to the engine thrust, and the ground system and its relation to the friction of the wheel system.

It is my opinion (and that of the USAF, and other pilots in the airline I now fly for) that Fx>Fy and that the airplane will be able to fly, with the caveat that the wheel speed will be twice as fast as the ground speed of the airplane. We are ignoring tire speed limitations and bearing limitations for the purpose of this thought problem.

I have noticed that some of the posters here are suffering from confirmation bias which skews the thought process.....stick with the physics and all will be well......

Hope this helps!

FM
Atl5p
QUOTE (krreagan+Feb 10 2006, 12:50 PM)
QUOTE (Atl5p+Feb 9 2006, 07:29 PM)
....get off my boat Kreegan before we hit a reef!!!

No worries, I would never, ever get on/in a motorized vehicle that you were driving/piloting!

Krreagan

grendle
Still going strong eh?

This whole argument boils down to which is more powerful: the thrust from the aircrafts engines or the friction between the aircraft and the ground / water.

If you rip the wheels off the plane will it take off even on a stationary belt? Most won't, but stick a big enough engine, or a rocket in it and it will ovecome the friction and take off.

All the moving belt / water does is add the equivalent of more friction.

Given enough thrust the plane will fly. Sure, maybe the wheel bearings will melt and the tires burst... but then so will the bearings in teh conveyor and the belt will shred.
Atl5p
QUOTE (Hidden_Tiger+Feb 10 2006, 09:16 AM)
QUOTE (krreagan+Feb 10 2006, 06:45 AM)
QUOTE (Atl5p+Feb 9 2006, 07:29 PM)
In so many ways, Kreegan, you are so wrong.....everything is wrong....this whole 'airboat' vs 'propboat' is a dream...

Are you really still trying to fight this fight Atl5p?! Stubborn ignorance at its worst!

I think at Atl5p is actually right with respect to the boats. In the water, velocities just do a straight vector addition, regardless of power source. However, frictional forces acting on wheels (of a car/plane) are in no way analogous to those acting on a boat, so Atl5p is wrong to use this analogy to prove anything about the plane senario.

So what you are saying is that it dosn't matter that the force comes from the 'wind' vs the 'propellor'? You'd better be hitting up Kreegan to get his permission before you cross him.

All you 'fly boys' need to get your stories straight.

Why don't we actually call a 'truce' between the fly vs nofly people.

It seems that the No Fly folks have their stories straight...

Do you Fly Boys actually have the balls to debate one another on your own differences of opinion?

So, in case you missed it, the 'fly boys' are in disagreement. Some feel that the motorsailer will behave differently while under prop power vs sail power.

Some feel that the motorsailer will behave the same either way.

Fly Boys, get your stories straight. You are begining to look pathetic.

The only conclusion is this:

'Water current' and 'treadmill' are the same principals.

On the water, sail vs prop....it dosn't matter...both will be affected the same.

On the treadbelt, wheels vs air....it dosn't matter....both will be affected the same.

Hey, you can still make that plane take off....all you have to admit is that the car will 'take off' and 'run up' the runway alongside the plane....go ahead, I'd like to hear it.
krreagan
QUOTE (Atl5p+Feb 10 2006, 07:55 PM)
QUOTE (krreagan+Feb 10 2006, 12:50 PM)
QUOTE (Atl5p+Feb 9 2006, 07:29 PM)
....get off my boat Kreegan before we hit a reef!!!

No worries, I would never, ever get on/in a motorized vehicle that you were driving/piloting!

Krreagan

Ignorance! What a pitty! Still trying to do battle with the windmill eh! Atl5p?

Being land locked I'll admit that my experience in boats is limited to a sunfish sail boat, a catamaran ocean racer, a deep sea fishing boat, several types of pontoon party barges and two aircraft carriers (Kitty Hawk and Nimitz).

It seems bret F has misinterpreted his observations, just as you have!

Krreagan
Atl5p
QUOTE (grendle+Feb 10 2006, 10:09 PM)
Still going strong eh?

This whole argument boils down to which is more powerful: the thrust from the aircrafts engines or the friction between the aircraft and the ground / water.

If you rip the wheels off the plane will it take off even on a stationary belt? Most won't, but stick a big enough engine, or a rocket in it and it will ovecome the friction and take off.

All the moving belt / water does is add the equivalent of more friction.

Given enough thrust the plane will fly. Sure, maybe the wheel bearings will melt and the tires burst... but then so will the bearings in teh conveyor and the belt will shred.

QUOTE
Given enough thrust, the plane will fly

Noo....given enough power, the treadbelt will send that plane backwards at 600mph....

That's the exact same bullshit you just spewed.....only I did it in the 'opposite direction'.

Remember, this isn't about 'who has more power'...this is about 'matching speeds'.
krreagan
QUOTE (Atl5p+Feb 10 2006, 08:24 PM)
QUOTE (Hidden_Tiger+Feb 10 2006, 09:16 AM)
QUOTE (krreagan+Feb 10 2006, 06:45 AM)
QUOTE (Atl5p+Feb 9 2006, 07:29 PM)
In so many ways, Kreegan, you are so wrong.....everything is wrong....this whole 'airboat' vs 'propboat' is a dream...

Are you really still trying to fight this fight Atl5p?! Stubborn ignorance at its worst!

I think at Atl5p is actually right with respect to the boats. In the water, velocities just do a straight vector addition, regardless of power source. However, frictional forces acting on wheels (of a car/plane) are in no way analogous to those acting on a boat, so Atl5p is wrong to use this analogy to prove anything about the plane senario.

So what you are saying is that it dosn't matter that the force comes from the 'wind' vs the 'propellor'? You'd better be hitting up Kreegan to get his permission before you cross him.

All you 'fly boys' need to get your stories straight.

Why don't we actually call a 'truce' between the fly vs nofly people.

It seems that the No Fly folks have their stories straight...

Do you Fly Boys actually have the balls to debate one another on your own differences of opinion?

So, in case you missed it, the 'fly boys' are in disagreement. Some feel that the motorsailer will behave differently while under prop power vs sail power.

Some feel that the motorsailer will behave the same either way.

Fly Boys, get your stories straight. You are begining to look pathetic.

The only conclusion is this:

'Water current' and 'treadmill' are the same principals.

On the water, sail vs prop....it dosn't matter...both will be affected the same.

On the treadbelt, wheels vs air....it dosn't matter....both will be affected the same.

Hey, you can still make that plane take off....all you have to admit is that the car will 'take off' and 'run up' the runway alongside the plane....go ahead, I'd like to hear it.

I'd worry when the disagreements are not there as they are a healthy part of scientific discussions. D'oh! I forgot you haven't had any scientific education yet, so all this must be above your head, sorry! If you'd like, we could wait 8-9 years for you to catch up so that you might put forth a reasonable argument!

Your ignorance is glaring Atl5p! I'd get any education in the physical sciences! as it is painfully obvious (over the last 270+ pages) that you are severely lacking in this area!

Krreagan
krreagan
QUOTE (Atl5p+Feb 10 2006, 08:30 PM)
QUOTE (grendle+Feb 10 2006, 10:09 PM)
Still going strong eh?

This whole argument boils down to which is more powerful: the thrust from the aircrafts engines or the friction between the aircraft and the ground / water.

If you rip the wheels off the plane will it take off even on a stationary belt?  Most won't, but stick a big enough engine, or a rocket in it and it will ovecome the friction and take off.

All the moving belt / water does is add the equivalent of more friction.

Given enough thrust the plane will fly.  Sure, maybe the wheel bearings will melt and the tires burst... but then so will the bearings in teh conveyor and the belt will shred.

QUOTE
Given enough thrust, the plane will fly

Noo....given enough power, the treadbelt will send that plane backwards at 600mph....

That's the exact same bullshit you just spewed.....only I did it in the 'opposite direction'.

Remember, this isn't about 'who has more power'...this is about 'matching speeds'.

Atl5p,
Therein lies your ignorance of the physics of the problem! you don't have the knowledge of physics to get to the heart of the issues and understand how to organize a physical description of what is going on in order to formulate a cogent solution to that problem!

Krreagan
Guest
QUOTE (Atl5p+Feb 11 2006, 03:24 AM)
QUOTE (Hidden_Tiger+Feb 10 2006, 09:16 AM)
QUOTE (krreagan+Feb 10 2006, 06:45 AM)
QUOTE (Atl5p+Feb 9 2006, 07:29 PM)
In so many ways, Kreegan, you are so wrong.....everything is wrong....this whole 'airboat' vs 'propboat' is a dream...

Are you really still trying to fight this fight Atl5p?! Stubborn ignorance at its worst!

I think at Atl5p is actually right with respect to the boats. In the water, velocities just do a straight vector addition, regardless of power source. However, frictional forces acting on wheels (of a car/plane) are in no way analogous to those acting on a boat, so Atl5p is wrong to use this analogy to prove anything about the plane senario.

So what you are saying is that it dosn't matter that the force comes from the 'wind' vs the 'propellor'? You'd better be hitting up Kreegan to get his permission before you cross him.

All you 'fly boys' need to get your stories straight.

Why don't we actually call a 'truce' between the fly vs nofly people.

It seems that the No Fly folks have their stories straight...

Do you Fly Boys actually have the balls to debate one another on your own differences of opinion?

So, in case you missed it, the 'fly boys' are in disagreement. Some feel that the motorsailer will behave differently while under prop power vs sail power.

Some feel that the motorsailer will behave the same either way.

Fly Boys, get your stories straight. You are begining to look pathetic.

The only conclusion is this:

'Water current' and 'treadmill' are the same principals.

On the water, sail vs prop....it dosn't matter...both will be affected the same.

On the treadbelt, wheels vs air....it dosn't matter....both will be affected the same.

Hey, you can still make that plane take off....all you have to admit is that the car will 'take off' and 'run up' the runway alongside the plane....go ahead, I'd like to hear it.

The car and plane will both run up to speed for liftoff...but since the car lacks wings, it will only maintain it's speed while the plane next to it will rise up off the belt and fly.
..of course this is with a plane of relatively low takeoff speed, and a car with good highend speed.
Hidden_Tiger
QUOTE (Atl5p+Feb 11 2006, 03:24 AM)
The only conclusion is this:

'Water current' and 'treadmill' are the same principals.

On the water, sail vs prop....it dosn't matter...both will be affected the same.

On the treadbelt, wheels vs air....it dosn't matter....both will be affected the same.

Hey, you can still make that plane take off....all you have to admit is that the car will 'take off' and 'run up' the runway alongside the plane....go ahead, I'd like to hear it.

I'd be happy to admit it. In fact I already did in my last post. The plane will fly, but a car will also gain speed in the same way. Think about it like Skader did - you can't have a stationary car (with respect to the ground) on a moving treadmill, that violates the conditions of the problem.

So Atl5p, are you now a 'Fly Boy' too?

The resolution of this thread is somewhat unnerving to me. Is there not ONE person in the forum who can confirm/refute my equations? Has anyone here taken Physics I or do you all just guess?
krreagan
QUOTE (Hidden_Tiger+Feb 11 2006, 12:40 AM)
QUOTE (Atl5p+Feb 11 2006, 03:24 AM)
The only conclusion is this:

'Water current' and 'treadmill' are the same principals.

On the water, sail vs prop....it dosn't matter...both will be affected the same.

On the treadbelt, wheels vs air....it dosn't matter....both will be affected the same.

Hey, you can still make that plane take off....all you have to admit is that the car will 'take off' and 'run up' the runway alongside the plane....go ahead, I'd like to hear it.

I'd be happy to admit it. In fact I already did in my last post. The plane will fly, but a car will also gain speed in the same way. Think about it like Skader did - you can't have a stationary car (with respect to the ground) on a moving treadmill, that violates the conditions of the problem.

So Atl5p, are you now a 'Fly Boy' too?

The resolution of this thread is somewhat unnerving to me. Is there not ONE person in the forum who can confirm/refute my equations? Has anyone here taken Physics I or do you all just guess?

I have taught college level physics in the past.

Atl5p's illogical arguments are worth about 180 of the 270+ pages in this thread (if not more), so I doubt there is any force in the universe that would convince him/her/it!

Admitting you are wrong is a sign of maturity and ultimatly an indication that knowledge is more important then being correct in an argument, So I wouldn't expect any admission from Atl5p!

Krreagan
Guest
I also admit.... that I posted some excerpts HOPING that Atl5p would come back to add spice to this eternal thread! It worked.....! More entertainment!
bret f
QUOTE (krreagan+Feb 11 2006, 03:30 AM)

Ignorance! What a pitty! Still trying to do battle with the windmill eh! Atl5p?

Being land locked I'll admit that my experience in boats is limited to a sunfish sail boat, a catamaran ocean racer, a deep sea fishing boat, several types of pontoon party barges  and two aircraft carriers (Kitty Hawk and Nimitz).

It seems bret F has misinterpreted his observations, just as you have!

Krreagan

No, I haven't misinterpreted anything, I think you've got it wrong.

Motor-driven yachts and sail-powered ones are effectively identical in purpose, regardless of whether the thrust is produced by air or not. Like I said, it's quite possible to be going backwards in relation to land in a sailboat if the current against you is strong enough.

Quote: "When planning a day's yachting in tidal waters, first look at the tide tables. It ought to be obvious that with a favorable two-knot tide, a yacht of four knots will be effectively three times as fast as when it is battling against the tide. Yet it is common to see boats struggling home against a tide as darkness falls. The right use of the tide will enhance any day's sailing. Get it wrong and you could be in for a miserable time and a long journey home."

In layman's terms, a boat with a 4 knot wind riding on a 2 knot current has a total speed of 6 knots in relation to land. If the boat is heading *against* the tide, it's total speed is reduced to 2 knots.

Calculate the total knots by adding the two vectors together, it's simple as that. Ergo, a boat with a 2 knot wind heading against a 2 knot current has a velocity of zero in relation to land.

As I said, I've done this myself and there's no question whether it's right or not. Tides and currents are one of the fundamental considerations when sailing on tidal waters.

There are current and tidal charts abound on the internet for this very reason, if you care to take a look. All sailors have to obey these charts to avoid getting marooned at sea when facing a current that's as strong as the wind at their backs.

They would never need these charts if they could bypass the currents by simply putting up the sails.

Air in the sails won't make a boat any more effective when facing against an opposing current. It's simple relativity. You just need to think of the forces involved then re-apply them to your logic.

krreagan
QUOTE (bret f+Feb 11 2006, 01:45 PM)
QUOTE (krreagan+Feb 11 2006, 03:30 AM)

Ignorance! What a pitty! Still trying to do battle with the windmill eh! Atl5p?

Being land locked I'll admit that my experience in boats is limited to a sunfish sail boat, a catamaran ocean racer, a deep sea fishing boat, several types of pontoon party barges  and two aircraft carriers (Kitty Hawk and Nimitz).

It seems bret F has misinterpreted his observations, just as you have!

Krreagan

No, I haven't misinterpreted anything, I think you've got it wrong.

Motor-driven yachts and sail-powered ones are effectively identical in purpose, regardless of whether the thrust is produced by air or not. Like I said, it's quite possible to be going backwards in relation to land in a sailboat if the current against you is strong enough.

Quote: "When planning a day's yachting in tidal waters, first look at the tide tables. It ought to be obvious that with a favorable two-knot tide, a yacht of four knots will be effectively three times as fast as when it is battling against the tide. Yet it is common to see boats struggling home against a tide as darkness falls. The right use of the tide will enhance any day's sailing. Get it wrong and you could be in for a miserable time and a long journey home."

In layman's terms, a boat with a 4 knot wind riding on a 2 knot current has a total speed of 6 knots in relation to land. If the boat is heading *against* the tide, it's total speed is reduced to 2 knots.

Calculate the total knots by adding the two vectors together, it's simple as that. Ergo, a boat with a 2 knot wind heading against a 2 knot current has a velocity of zero in relation to land.

As I said, I've done this myself and there's no question whether it's right or not. Tides and currents are one of the fundamental considerations when sailing on tidal waters.

There are current and tidal charts abound on the internet for this very reason, if you care to take a look. All sailors have to obey these charts to avoid getting marooned at sea when facing a current that's as strong as the wind at their backs.

They would never need these charts if they could bypass the currents by simply putting up the sails.

Air in the sails won't make a boat any more effective when facing against an opposing current. It's simple relativity. You just need to think of the forces involved then re-apply them to your logic.

Your analogies are ignorant when trying to compare them to the question at hand. The frictional components of the water against the hull, is no where near the friction of the wheels.

Your misinterpretation is in how they relate (or do not relate) to this problem at hand! Trying to solve this question by making it harder and more complex is illogical!

A closer analogy would be a hovercraft, Do the water currents have much impact on the hovercraft? almost none (assuming a smooth water surface)! The wind has a greater impact on a hovercraft then water currents do.
The hovercraft moves in relation to the air, not the water!
The plane moves in relation to the air, not the ground!

Krreagan
mr voo
it takes off unless the brakes are on the wheels or unless its already travelling backwards too fast on the belt.
swimmer
QUOTE (Atl5p+Feb 11 2006, 03:30 AM)
Noo....given enough power, the treadbelt will send that plane backwards at 600mph....

That's the exact same bullshit you just spewed.....only I did it in the 'opposite direction'.

Remember, this isn't about 'who has more power'...this is about 'matching speeds'.

Holding that thought ATL5P - please tell us how the conveyor/treadbelt can "send the plane backwards at 600mph"?

The friction between plane and treadbelt is limited by the weight of the plane (massXgravity) - so that limits the force the conveyor can apply to the plane.

The plane's engines in contrast are firmly attached and so the force they apply to the plane is only limited by the engines.
bret f
QUOTE (krreagan+Feb 12 2006, 12:04 AM)
A closer analogy would be a hovercraft, Do the water currents have much impact on the hovercraft? almost none (assuming a smooth water surface)! The wind has a greater impact on a hovercraft then water currents do.
The hovercraft moves in relation to the air, not the water!
The plane moves in relation to the air, not the ground!

Krreagan

A hovercraft is a very poor analogy here, because it bears no resemblance to an aircraft whatsoever. I'm surprised you've said this, because if you've taught physics you should already know they're completely different and it's pointless comparing them.

Hovercraft do not rely on airspeed or aerodynamics to gain lift, they use vertical thrust. They don't even touch water so they bear no relevance to this question.

Planes use forwards thrust to gain lift, provided by air. So the best analogy to use here would be a boatplane on water, heading upstream against a current.

Put a sail on the boatplane, and apply air to thrust it forwards on the water. With a 70 knot wind and a 70 knot current the plane's still going to have a zero-knot velocity in relation to land.
Guest
QUOTE (bret f+Feb 12 2006, 03:52 PM)

Put a sail on the boatplane, and apply air to thrust it forwards on the water. With a 70 knot wind and a 70 knot current the plane's still going to have a zero-knot velocity in relation to land.

Do you mean a windspeed of 70 knots? or a windspeed that propels/pushes the boat at 70 knots? there's a big difference.
A windspeed to move the boat at 70 knots will have to be very much more to overcome the hull friction.
bret f
QUOTE (Guest+Feb 12 2006, 04:41 PM)
QUOTE (bret f+Feb 12 2006, 03:52 PM)

Put a sail on the boatplane, and apply air to thrust it forwards on the water. With a 70 knot wind and a 70 knot current the plane's  still going to have a zero-knot velocity in relation to land.

Do you mean a windspeed of 70 knots? or a windspeed that propels/pushes the boat at 70 knots? there's a big difference.
A windspeed to move the boat at 70 knots will have to be very much more to overcome the hull friction.

OK. I mean a windspeed that would normally push it at 70 knots on a calm lake, or a river without a current. Same as a boatplane using air to push it at 70 knots across a lake.
isfn
QUOTE (bret f+Feb 12 2006, 03:52 PM)
QUOTE (krreagan+Feb 12 2006, 12:04 AM)
A closer analogy would be a hovercraft, Do the water currents have much impact on the hovercraft? almost none (assuming a smooth water surface)! The wind has a greater impact on a hovercraft then water currents do.
The hovercraft moves in relation to the air, not the water!
The plane moves in relation to the air, not the ground!

Krreagan

A hovercraft is a very poor analogy here, because it bears no resemblance to an aircraft whatsoever. I'm surprised you've said this, because if you've taught physics you should already know they're completely different and it's pointless comparing them.

Hovercraft do not rely on airspeed or aerodynamics to gain lift, they use vertical thrust. They don't even touch water so they bear no relevance to this question.

Planes use forwards thrust to gain lift, provided by air. So the best analogy to use here would be a boatplane on water, heading upstream against a current.

Put a sail on the boatplane, and apply air to thrust it forwards on the water. With a 70 knot wind and a 70 knot current the plane's still going to have a zero-knot velocity in relation to land.

A hovercraft is an excellent analogy, and the fact that it doesn't touch the water is why it's a good analogy. The question has nothing to do with lift and aerodynamics, the crux of the question is whether or not a moving surface (flowing river/conveyor belt) can prevent a vehicle (hovercraft/plane) from moving forward. And the answer is no because in each case there is very little friction between the two.
krreagan
QUOTE (bret f+Feb 12 2006, 08:52 AM)
QUOTE (krreagan+Feb 12 2006, 12:04 AM)
A closer analogy would be a hovercraft, Do the water currents have much impact on the hovercraft? almost none (assuming a smooth water surface)! The wind has a greater impact on a hovercraft then water currents do.
The hovercraft moves in relation to the air, not the water!
The plane moves in relation to the air, not the ground!

Krreagan

A hovercraft is a very poor analogy here, because it bears no resemblance to an aircraft whatsoever. I'm surprised you've said this, because if you've taught physics you should already know they're completely different and it's pointless comparing them.

Hovercraft do not rely on airspeed or aerodynamics to gain lift, they use vertical thrust. They don't even touch water so they bear no relevance to this question.

Planes use forwards thrust to gain lift, provided by air. So the best analogy to use here would be a boatplane on water, heading upstream against a current.

Put a sail on the boatplane, and apply air to thrust it forwards on the water. With a 70 knot wind and a 70 knot current the plane's still going to have a zero-knot velocity in relation to land.

Bret F,
The fact that you feel a hovercraft is a bad analogy compared to any type of boat, illustrates your lack of understanding of the physics involved in the original question, and how to use similar examples to prove/disprove theoretical questions posed.

Both the plane and hovercraft use air breathing engines (props or jets). Both have very little frictional interaction with the surface that they are dependent on (wheels on a tarmac or belt for the plane, an air cushion on water or land for the hovercraft). This question has nothing to do with lift from the planes wings except to illustrate that the plane is moving forward into the air mass. The question could just a easily have said a jet (thrust) powered car reaches 200mph instead of a plane taking off. The central concept would have been exactly the same.

Krreagan
Fynlcut
QUOTE (bret f+Feb 12 2006, 04:57 PM)
QUOTE (Guest+Feb 12 2006, 04:41 PM)
QUOTE (bret f+Feb 12 2006, 03:52 PM)

Put a sail on the boatplane, and apply air to thrust it forwards on the water. With a 70 knot wind and a 70 knot current the plane's  still going to have a zero-knot velocity in relation to land.

Do you mean a windspeed of 70 knots? or a windspeed that propels/pushes the boat at 70 knots? there's a big difference.
A windspeed to move the boat at 70 knots will have to be very much more to overcome the hull friction.

OK. I mean a windspeed that would normally push it at 70 knots on a calm lake, or a river without a current. Same as a boatplane using air to push it at 70 knots across a lake.

The problem you are having is the definition of speed for each vehicle.
I'm not very boat savy, but I believe a boats speed is measured by the speed that water passes it's hull. (i.e. something like an impeller pointed in the direction of movement, correct me if I am wrong please.)

A car's speed indicator tells you how fast the road is passing under the car.

A plane speed indicator tells you how fast the air is moving past the plane.

If a plane takes of at 70kts, this is a 70kts AIRSPEED.
If a boat travels at 70kts, this is its WATER speed.
If a car drives at 70kts, this is its GROUND speed.

In calm air, a plane doing 70kts, on a runway, in the water, or in the air, is still traveling at 70kts AIRSPEED.

NOT water speed, and NOT ground speed.
Tell me how "ground speed is the speed of the plane when it is on the ground" and I'll tell you to go back many pages and see the effects altitude, temperature, humidity, and a host of other things will allow a plane to move across the ground at a airspeed that does not match it's ground speed.

So by using the speed indicator provided with each vehicle they can move no faster than the medium in which the speed is derived.

A plane will not make forward progress if it flies at 70kts in a 70kts headwind.
A boat can make no progress in a 5kts current if it moves at 5kts.
And alas a car can make no progress if it drives at 90mph on a conveyor moving at 90mph.

Now measure each with the standard speed indicators again.
Put a bass boat in the wind tunnel (in a big pool), if the boat's speed indicator registers 70kts, and the wind is a 70kts headwind is it moving forawrd?
Put the car in a river (pretend it can maintain traction and run underwater). Its speed indicator registers 50mph, the current is moving at 20 mph, how long will it take to drive 50 miles?
Now put the airplane on a conveyor. The conveyor is moving at 40kts one way. The plane's speed indicator measures 40kts traveling in the other direction. Is the plane moving?

QUOTE
Do you mean a windspeed of 70 knots? or a windspeed that propels/pushes the boat at 70 knots?  there's a big difference.
A windspeed to move the boat at 70 knots will have to be very much more to overcome the hull friction.

Again I might be wrong, but I'm pretty sure a sailboat can out run the wind.
krreagan
QUOTE
Again I might be wrong, but I'm pretty sure a sailboat can out run the wind.

My sailing experience is very limited as well... I don't see how a sailboat can out run the wind? the boat can have a speed over the water faster then the wind, but I don't think it can "out run" the wind!

Krreagan
Fynlcut
QUOTE (krreagan+Feb 13 2006, 02:09 PM)
QUOTE
Again I might be wrong, but I'm pretty sure a sailboat can out run the wind.

My sailing experience is very limited as well... I don't see how a sailboat can out run the wind? , but I don't think it can "out run" the wind!

Krreagan

Poor wording I guess, What I ment was it just as you said. "the boat can have a speed over the water faster then the wind"
To out run the wind would be impossible if the wind is your means of propulsion. But I do know ice boats can run well over 100mph in winds much less than that
sooks
Alright... the difference you guys are missing on the boat thing...and esp with the sailboat. is the sailboat has a huge a\$\$ F**king rudder sticking way into the water. not to mention how much deeper the hull sits in the water. when you have tht much hull in there.. the current actually has something to push on, THAT has nothing to do with friction... there, it actually has a force. now with the fan boat (the type they use in like hte everglades and whatnot..) your talking a light flat bottomed hull. that sits very shallow in the water... the current now cannot impart that force anymore (or very little) and the only thing that can be exerted is only friction much like the plane. which is minimal
Pr1moCL
lol, it has taken me awhile but I have read about the first 100 pages of this topic, finding it funny most of the time, and I cant believe this thing is still going!! Is everyone still on simply whether or not the plane will take off? Because I want to get started in this topic, it seems fun.
egnorant
It flies!
Plane moves one direction and the belt moves the other.
Confusion ensues when claims are made that the plane won't move!
The question states that the plane moves...
Then claims are made that the belt will hold it back.....
This is of course ridiculous as the plane was designed to overcome the directional forces transferred through the wheels (and inertia).
Then everyone chimes in with the "what if?" and change the question to PROVE it won't fly.
"Experts" then come on and make silly claims.
Then the silly folk show up to tease the more anal of the "will fly" crowd.
Analogies abound and soon it is a submarine pulled by birds on ice while resting on a hovercraft.
I actually see it winding down a bit as the Silly people have annoyed the die hard "will fly" teachers into quitting.
Then people show up from other forums to see the name calling and silly comparisons.
Throw in a dissertation on force vectors and friction modifiers and you are up to date!!
Simple word problem that has blown up because people won't admit that the plane moves relative to its own starting point......and spinning wheels ain't movement!
That is why they have the saying about "Just spinning your wheels" it denotes a lot of activity with no movement.
Bruce
(I was hoping for 300 pages myself!)
Fynlcut
We are only 20 pages away. Things have slowed but I bet it gets there.
Guest
This thread, along with the countless others like it scattered across the internet, has the potential to prove that there is an endless supply of idiots in existence on this planet. Or that idiocy is contagious. No matter how many times it is explained using basic physics, there's always another idiot that comes along, ignorant of the physics involved, starting the same old argument all over again. Maybe you idiots should worry about other things, like arguing that the world is really flat, or that the universe revolves around Earth, etc.
Guestion
^^^^ So, uhh, which side are you on?
Guest
QUOTE (Guestion+Feb 14 2006, 02:04 PM)
^^^^ So, uhh, which side are you on?

I'm on the side that realizes Newtonian physical laws are true and also understands them. The side that knows the difference between weight and mass, and the difference between acceleration and speed. The side that knows what the Law of Conservation of Momentum is and why it applies to this problem. The side that knows what a free body diagram is and how it can be used to illustrate the forces present on the plane. The side that understands that the speed of the plane and the speed of the conveyor belt are part of the problem only because of the relationship between force, mass, and acceleration. The side that has enough knowledge of the physics involved to demonstrate their conclusion rather than spewing neverending bullshit at a rate that makes it nearly impossible to counter due to the sheer number of fallacies perpetuated.
Guest
QUOTE (sooks+Feb 13 2006, 09:41 PM)
Alright... the difference you guys are missing on the boat thing...and esp with the sailboat.  is the sailboat has a huge a\$\$ F**king rudder sticking way into the water.  not to mention how much deeper the hull sits in the water.  when you have tht much hull in there.. the current actually has something to push on, THAT has nothing to do with friction... there, it actually has a force.  now with the fan boat (the type they use in like hte everglades and whatnot..)  your talking a light flat bottomed hull.  that sits very shallow in the water... the current now cannot impart that force anymore (or very little)  and the only thing that can be exerted is only friction much like the plane.  which is minimal

So you could put a fanboat on a river next to a normal boat without either of them applying any thrust, and the fanboat would be getting affected very little by the current and would be moving downstream at a much slower rate because of it's flat bottom and because the river can only impart 'minimal' friction on it compared to the 'normal' boat.

And you could put a folded paper boat on the river and it'd be travelling even slower still...because it's so light and it's not actually sitting 'in' the water like a normal boat...so the current must have almost no effect on it whatsoever............
sooks
yeah for the most part tahts what im saying (aside from the paper boat comment).... but youve got to keep in mind. this situation doesnt really occur in real life because for what im talking about its perfectly calm water that still has a current. as soon as you have waves and such, it acts on the boat. and the boats still do sit in the water so it does act on them. its not huge differnces between the two..but there is slight differences

and being light, has nothing to do with sitting in the water... you could make a boat out of cement that could float in less water than something of plexiglass..... its all buoyancy... and i thought you were all about hte physics..
Guest
Lets look at this problem using a snowboard with the snowboarder wearing wings(hanglider wings) as he descnds the slope, he picks up speed given that the slope is great enough to overcome the minimal friction induced by the contact of snowboard and the snow itself. If the board was coated with red wax, would he be able to move forward and accelerate to a speed where the wings would provide lift? At what temperature would this "lift" occur. Figure the slopes movement based on the rotation speed of the earth. How fast would the snowboarder have to travel before the snow"conveyor" speed was matched... would he be able to match this speed before he lifted off?
isfn
QUOTE (Guest+Feb 14 2006, 05:34 PM)
Lets look at this problem using a snowboard with the snowboarder wearing wings(hanglider wings) as he descnds the slope, he picks up speed given that the slope is great enough to overcome the minimal friction induced by the contact of snowboard and the snow itself. If the board was coated with red wax, would he be able to move forward and accelerate to a speed where the wings would provide lift? At what temperature would this "lift" occur. Figure the slopes movement based on the rotation speed of the earth. How fast would the snowboarder have to travel before the snow"conveyor" speed was matched... would he be able to match this speed before he lifted off?

It depends, is there a full moon?
Guest
"We are only 20 pages away. Things have slowed but I bet it gets there. "

Lets throw a party.

krreagan
QUOTE (Guest+Feb 14 2006, 09:31 AM)
QUOTE (sooks+Feb 13 2006, 09:41 PM)
Alright... the difference you guys are missing on the boat thing...and esp with the sailboat.  is the sailboat has a huge a\$\$ F**king rudder sticking way into the water.  not to mention how much deeper the hull sits in the water.  when you have tht much hull in there.. the current actually has something to push on, THAT has nothing to do with friction... there, it actually has a force.  now with the fan boat (the type they use in like hte everglades and whatnot..)  your talking a light flat bottomed hull.  that sits very shallow in the water... the current now cannot impart that force anymore (or very little)  and the only thing that can be exerted is only friction much like the plane.  which is minimal

So you could put a fanboat on a river next to a normal boat without either of them applying any thrust, and the fanboat would be getting affected very little by the current and would be moving downstream at a much slower rate because of it's flat bottom and because the river can only impart 'minimal' friction on it compared to the 'normal' boat.

And you could put a folded paper boat on the river and it'd be travelling even slower still...because it's so light and it's not actually sitting 'in' the water like a normal boat...so the current must have almost no effect on it whatsoever............

Ignorance is rampant!

The amount of force to overcome the force of the flowing water is (or to move a boat in still water) much less for a fan boat then a normal hulled boat! When the only force acting against either boat is the water flow, both will behave similarly When the water flow is being countered by thrust from a prop or fan, the fan boat (flat bottom) will require much less force to overcome the force of the water

Krreagan

Oops, Sorry, I missed the sarcasm in that post!
Guest
lol, you're right. They've been doing it wrong all along. Flat bottom boats are sooo much better against currents than any other type of design.

And what happens if you put a sail on your flat-bottomed fanboat? Does it still move slower than a fan-powered one just because it's a sail?

Guest
heh! I just realized we can control the google ads listed below.....they've gone from conveyors to trains, to boats,..... and who knows what else !
Guest
QUOTE (Guest+Feb 14 2006, 09:29 PM)
heh! I just realized we can control the google ads listed below.....they've gone from conveyors to trains, to boats,..... and who knows what else !

I don't think the helicopter discussion was long enough for ads to show up, the aircraft carrrier might have swayed the ads somewhat, the motorcycle may have altered the ad direction but don't know. Did anyone notice any ads about the skateboards?
Guest
QUOTE (Guest+Feb 14 2006, 08:28 PM)
lol, you're right. They've been doing it wrong all along. Flat bottom boats are sooo much better against currents than any other type of design.

And what happens if you put a sail on your flat-bottomed fanboat? Does it still move slower than a fan-powered one just because it's a sail?

if you put your giant sail on a flat bottomed boat it would probably tip over because it doesnt have a rudder to stabalize it... and no.. it wouldnt move slower than a fan one if the wind was pushing a sail on the same boat at the same force as the fan pushed backwards..
Guest
QUOTE (Guest+Feb 14 2006, 09:51 PM)
if you put your giant sail on a flat bottomed boat it would probably tip over because it doesnt have a rudder to stabalize it... and no.. it wouldnt move slower than a fan one if the wind was pushing a sail on the same boat at the same force as the fan pushed backwards..

Then how is it any less likely to tip over with a big fan on the back? Still no rudder.

But if they are both the same and the boat was something like this then the result would be the same in both cases - whether it's a fan or a sail, they'd both be affected equally by an opposing current, and neither would make any progress upstream.
Pr1moCL
Not if the fan motor was running at a sufficient enough speed, or the wind was blowing sufficiently...Which are both always possible.
Guest
Oh yes, you're absolutely right. In that case they would obviously be able to move fowards.

But in the sceario of the current always matching the wind or fan force, then they'd not gain any ground upstream.
sooks
This is such a dumb argument. What are we getting at by comparing a sailboat to a fan boat. All i was saying from my points is that a fan boat sits atop the water and the only thing affecting it was friction. Its not a perfect example because all the boats sit somewhat into the water where the current can affect them. the fact is, the belt cant act upon the plane only through friction which isnt as great as the thrust force.
Guest
QUOTE (sooks+Feb 15 2006, 12:36 AM)
This is such a dumb argument. What are we getting at by comparing a sailboat to a fan boat.  All i was saying from my points is that a fan boat sits atop the water and the only thing affecting it was friction.  Its not a perfect example because all the boats sit somewhat into the water where the current can affect them.  the fact is, the belt cant act upon the plane only through friction which isnt as great as the thrust force.

Oh...THIS is a dumb argument...but not the last 270 pages!!
Pr1moCL
lol, pretty much everyone is right, they are just looking the plane, sailboat, fanboat, snowboard ETC......in a different way. If the plane was on its belly, it would almost be impossible for it to overcome the friction of the conveyor, especially under its own power.
Guest
QUOTE (Pr1moCL+Feb 16 2006, 04:20 AM)
lol, pretty much everyone is right, they are just looking the plane, sailboat, fanboat, snowboard ETC......in a different way. If the plane was on its belly, it would almost be impossible for it to overcome the friction of the conveyor, especially under its own power.

But if you applied a high viscosity grease to the conveyor, and teflon-coated the belly, the friction would be reduced.
Pr1moCL
Your right, it would most likely be able to take off then...
egnorant
Had a little time to kill.
Here are some questions that I am throwing around...

Can you tune the belt to move at half the speed of the plane?

If I jack up the plane and spin the wheels at 100MPH how fast is the plane moving?

Are there any conditions that can allow the plane to take of with a speed of zero?

If you get on a conveyor belt moving at 10 MPH and walk at 10 MPH in the same direction, how far have you moved in an hour?

If I fly a plane at 200 MPH over a belt moving in the opposite direction at 200MPH,
what is the speed of the plane?

When I throw a baseball, am I moving away from the baseball or is the baseball moving away from me?

Bruce
Still want to hit 300!
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