Maybe they should save $ by shutting down that welfare agency for the intelligentsia

**called LIGO**.

You probably meant to say the government welfare agency called public University tenure for professors.

QUOTE

(LIGO) results have failed to produce a thing.

Sure it did.... it produced "NULL results".

And think about all the non-governmental industry that benefited... like the private industry concrete manufacturer who had to fabricate miles of concrete tunnels...

http://upload.wikimedia.org/wikipedia/comm...Reservation.JPG...and all the new buildings that had to be designed and constructed by hardworking hard hats getting paid over-time.... ..and all the asphalt roads that needed to be constructed to reach these sites:(isn't it worth a few hundred mil dollars just to upset the environMENTAL wachos?)

http://atlasobscura.com/place/ligo-livingston-observatoryhttp://www.ligo.org/multimedia/gallery/lho...ges/Aerial4.jpg....and all the extra Terra-bytes of hard drives that had to be purchased to crunch all the data runs.

....and just think about all the Domino Pizza delivery guys that got extra tips for delivering free pizzas (exceeding the 30 minute guarantee) to all those dead heads out there in nowhere-ville miles from grocery stores ...

http://www.ligo.org/multimedia/gallery/lho...ges/Aerial5.jpgSee; isn't federal government socialism wonderful?

Lunar

Matador

22nd April 2010 - 04:24 AM

Can somebody please clear this up? A couple of posters have stated that 'pound' is a measure of force, and that it has gravity already 'built' into it.

As far as i can see, the pound in the original question referred to

*mass* as otherwise the unit of

lbf would have been used.

Reading the wiki entry on 'pound'

http://en.wikipedia.org/wiki/Pound_(mass)QUOTE

The pound or pound-mass (abbreviation: lb, lbm) is a unit of mass used in the imperial, United States customary and other systems of measurement. A number of different definitions have been used, the most common today being the international avoirdupois pound of exactly 0.45359237 kilograms.

NoCleverName

22nd April 2010 - 10:45 AM

QUOTE (Matador+Apr 22 2010, 12:24 AM)

Can somebody please clear this up? A couple of posters have stated that 'pound' is a measure of force, and that it has gravity already 'built' into it.

You don't measure a rocket engine's reaction force in

*kilograms* do you? You'll hear it referred to as

*pounds of thrust*. In SI units it's the

*newton*.

You'll often hear that someone weighing "180 pounds" on earth will weigh but "30 pounds" on the moon. You don't hear about them losing 70 or so kilos, though, do you?

I can't help it that sloppy terminology has entered common language.

In the OP a weight of "4000 pounds" was mentioned and you had to calculate a potential energy PE=mgh. Now, if the problem mentioned a mass of 1800kg then you would immediately multiplied by 9.8m/s^2 to handle the "mg" term. But in "pounds", would you have multiplied by 32fps^2 to handle "mg" (staying in english units)? No.

Observe you suggested dividing by 2.2 and then multiplying by 9.8. But what were the units of that "2.2"? They were "pounds per kg". And if you carefully backtrack the units of PE=mgh using the conversion factor you will find that "pounds" aren't really a unit of mass since there's an acceleration built in.

Start with

CODE

lb*ft = M*g*h

on the right substitute g=m*s^-2, h=m

on the left ft=c*m (conversion factor "c" feet per meter)

solve for lb and you get something in the form

lb = (M*m*s^-2)/c

which is essentially F = Ma

Limon

24th April 2010 - 09:34 PM

Yep: NoCleverName is correct.

A kilogram is a unit of mass, a newton is a units of force. The average gravitational force exerted upon (or by) a kilogram is 9.81 newtons on the Earth’s surface.

(4000 lb / 2.2) 1,818 kilograms is 17,835 newtons.

I believe Potential Energy is force (newtons) times distance (meters). A joule is a newton meter.

200 ft * .3048 = 60.96 meters

17,835 newtons * 60.96 meters = 1,087,222 joules

Now lets check our math. d = ½ v²/a, 60.96 meter = .5 * v * v / 9.81 m/sec/sec; or, 60.96 * 2 * 9.81 = v², or v = 34.58 m/sec

Ke = ½ m v² or .5 * 1818 kg * 34.58 m/sec * 34.58 m/sec =1,087,078 joules.

Looks like it is correct because PE before the fall is equal to Ke after the fall.

Now if you are going to use the English system you will have to become familiar with Slug (mass), pound (force) 32 ft/sec/sec (gravitational accelerate) and v in feet per sec.

But it is easier to just convert joules to foot pounds.

Limon

27th April 2010 - 12:52 AM

I found out something rather interesting.

Microsoft has a program called ‘convert’ that converts one unit into another unit (feet to meters; joules to pound-feet; liters to quarts etc). It is quite comprehensive. I was very surprised to see that Microsoft does not know what a slug is. Slug was not listed in the units of mass. Now I do not believe every thing I read, so I was not dismayed, but this little over sight was very interesting. And maybe warrant of a little thought.

4000 pounds at a height of 200 feet is 800,000 foot points of energy. PE = distance times force.

If an object is dropped 200 feet it will have a velocity of 113.44 feet per second. d = ½ * v² / a a = 32.17 ft/sec/sec, d is 200 ft

Ke = 1/2mv²: So this should be a true statement if pound is a mass. 800,000 ft-lbs = ½ * 4000 lb * 113.44 ft/sec * 113.44 ft/sec, but the product is much too high 25,737,267.

This proves that pound is not a mass. 25,737,267 / 800,000 = 32.17. The product needs to be divided by 32.17. Or 4000 / 32.17 = 124.34 slugs.

I am guessing that a slug has a mass that is equal to 32.17 pounds of force on the Earth surface. This happens to be the rate of gravitational acceleration (in feet per sec. per sec.) in the English system as 9.81 m/sec/sec is in the metric system. And the kilogram has a mass that is equal to 9.81 units of force (newtons) on the Earths surface.

It looks like Man set the meter as a unit of distance. He then set the cubit decimeter as a unit of volume. He set the cubit centimeter (of water) as a unit of mass. The unit of force necessary to accelerate one kilogram at a rate of one meter per second per second was called a newton. The gravitational force of the Earth exerts 9.81 such newtons of force upon one kilogram.

Something similar must have been done in the English system.

“From Diamond; Fundamental Concepts of Modern Physics” ‘One slug is the mass that will experience an acceleration of 1 ft/sec² when under the influence of an unbalanced force of one pound’.

But the scientific community (at least Microsoft) does not even know what a slug is. So it is probably time to drop the system.

NoCleverName

27th April 2010 - 12:58 AM

Got something right, Limon.

Now if we can just break you out of your nutty ideas about angular momentum.

Limon

28th April 2010 - 12:26 AM

Angular momentum conservation does not work in the lab. And energy can be made from gravity. There are holes in physics that you can drive a bus through. I am building trebuchets using only a wheel. Moderate increases in velocity make large increases in distance. The wheel/trebuchet (as it opens) is not conserving energy it is conserving linear Newtonian momentum.

NoCleverName

28th April 2010 - 01:10 AM

QUOTE (Limon+Apr 27 2010, 08:26 PM)

Angular momentum conservation does not work in the lab. And energy can be made from gravity.

Yup, that's our ol' Limon!

wwwnice

28th April 2010 - 01:34 AM

i have no idea about it, tady i am happy very much .

beause i brought very cheap products from

http://www.homybuy.com
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