TuxDave
Lifer
- Oct 8, 2002
- 10,571
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Originally posted by: giantpinkbunnyhead
Originally posted by: TuxDave
Imagine a treadmill with a wagon sitting on it and you're standing off the treadmill. You turn on the treadmill to like 10mph and you keep your hand on the back of the wagon to prevent it from falling off. The force that your hand exerts is equivalent to the thrust of the airplane. So it's possible to create a system where a plane is exerting thrust and isn't moving relative to air.
This is of course with the assumption that you have to exert some force to prevent the wagon from falling off. Otherwise if the necessary force to keep the wagon on the track equals zero, then such a system can't exist.
Faulty logic. If your hand's force merely keeps the wagon stationary on the treadmill, you are exerting the same force against the wagon as the treadmill exerts against it in the opposite direction. But the thrust from a jet would be far stronger than the force the conveyor belt could exert, just like you can apply more force to your hand and "push" the wagon further upstream.
If you plot treadmill speed versus necessary force to keep it stationary and if you're telling me that force will limit to some asymptotic value as treadmill speed goes to infinity, then you are correct that if you exert a force greater than that asymptotic value then the conveyor can never go fast enough. If that's not true, then you are not correct.