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Ok. A hypothetical question. A plane is on a giant treadmill type thing, designed to match the exact speed of the wheels, only going in reverse. Can it take off?


My answer is yes, but Ill let you guys figure it out before i justify myself.

Definately not. A jet engine powered plane in that circumstance would only pull air through the engines, and not over the entire wing. Resulting in no lift. A prop plane would also not take off, as it wouldn't be pulling air over the entire surface of the wings either.

Think harder.

Potter stop messing with people







actually i find it quite amusing

either explain your broken physics or go to hell

edit google wins all including my heart
http://answers.google.com/answers/threadview?id=428718

sam wrote:either explain your broken physics or go to hell

edit google wins all including my heart
http://answers.google.com/answers/threadview?id=428718

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? google says no answer at this time rofl. IT WILL GO VROOM AND FLY

I think this question is too vague. They need to specify the kind of plane as well as the variables of the area around. If there's any sort of gust of wind in any direction the plane would not take off at all. If the plane had props instead of engines it would have to get going at a much higher speed just to create enough thrust to lift itself.

if such a thing were physically true they would have invented a solution to use in airports as it'd be much safer to do a stationary launch of a huge ass jet air plane.

LOL. Yea that would be cool, stationary take off. But your thinking too inside the box. Its not talking about stationary take off. Its saying the treadmil is basicly as long as a runway, and can the jets or props wichever one, create thrust and push it forwarsd like they normalyl do, or will somehow the treadmill stop it by counteracyting the freerolling wheels. Forget all the wind variables, its just asking can it get up to speed.

But it can't create thrust, just because the wheels are spinning on the jet/whatever doesn't mean the jet is moving. And if the jet isn't moving, thrust won't be made.

I think thats right, though I haven't taken physics in forever.

what do you mean it cant create thrust? planes dotn take off by the wheels spinning, there there and freerolling to suspend it off the ground. The jets or proppeler create thrust.


how do you think the planes that land and take off in water with skis work? the propeler creates thrust.

Potter wrote:how do you think the planes that land and take off in water with skis work? the propeler creates thrust.

yes, but since it can actually move forward it can generate lift on the wings and take off.

If there was a complete lack of friction, then yes, the plane would be able to take off, as the treadmill would simply spin the wheels, but not put any thrust on the plane. However, because of gravity and friction, even though it's on wheels, the plane would get pushed backwards by the treadmill. This, of course, would be cancelled out by the plane's engines, which would be creating the same amount of forwards thrust.

Now, you may argue that the engine's thrust would be greater than the force of the treadmill, but that's not true. In the hypothetical scenario you proposed, the treadmill is set to automaticly match the speed of the wheels. Because of this, as the engine continued to push the plane forwards, the treadmill would continue to accelerate in order to cancel out the speed of the wheels. This, in turn, would result in both the rotation of the wheels and the tradmill to continuously accelerate. Now, in a real situation, either the treadmill would reach a point where it couldn't accelerate any more, or the wheels would spin so fast that they'd break or melt. However, this is a hypothetical situation, so both the wheels and the treadmill would keep accelerating infinately, while the plane never moves from it's original position, and therefore never takes off.

WhiteDragon wrote:If there was a complete lack of friction, then yes, the plane would be able to take off, as the treadmill would simply spin the wheels, but not put any thrust on the plane. However, because of gravity and friction, even though it's on wheels, the plane would get pushed backwards by the treadmill. This, of course, would be cancelled out by the plane's engines, which would be creating the same amount of forwards thrust.

Now, you may argue that the engine's thrust would be greater than the force of the treadmill, but that's not true. In the hypothetical scenario you proposed, the treadmill is set to automaticly match the speed of the wheels. Because of this, as the engine continued to push the plane forwards, the treadmill would continue to accelerate in order to cancel out the speed of the wheels. This, in turn, would result in both the rotation of the wheels and the tradmill to continuously accelerate. Now, in a real situation, either the treadmill would reach a point where it couldn't accelerate any more, or the wheels would spin so fast that they'd break or melt. However, this is a hypothetical situation, so both the wheels and the treadmill would keep accelerating infinately, while the plane never moves from it's original position, and therefore never takes off.

Thank you. I was trying to figure out how I'd word it, and this is similar to my thinking.

No, the engine wouldent just sit there and thrust, while the plane goes nowhere. The wheels are FREEROLLING, the ground can do whatever the hell ti wants, the plane will move forward. Yes, the wheels wil be spinning hella fast by the time it takes off, but it will go. think about it. millions ogf pounds of thrust and the plane is stationary, law of physics, where the hell is all that energy going?

Potter wrote: think about it. millions ogf pounds of thrust and the plane is stationary, law of physics, where the hell is all that energy going?

Yes, and the laws of physics say that it cannot lift off because there is not any lift on the wings other than a slight breeze that would be present. The energy is making the plane go forward, but as you stated in your first post the treadmill or other contraption that it is on is going fast enough to match the speed, making it not have any net movement. Energy is being expended.
Let me relate it to something you are more familiar with: If you're on a treadmill with a bike pedaling and the treadmill is matching your speed you wouldn't go anywhere. Now you don't have a jet engine, but you are pedaling. You aren't attempting to fly, but you still wont move forward.

If there is some way that anyone knows of for a plane to take off without any lift then post it. Otherwise: not probable(maybe possible, I've never taken a physics class so I'm not in the know).