Quote:
Originally Posted by fluxquanta
If the wheel bearings have "very little" or no friction, like you're suggesting, then yeah, the force due to the treadmill on the plane would be minimal, assuming everything's already in motion. What's the point of having the treadmill at all in this case?
There will be friction, though, and it wouldn't necessarily be small. I mean, you can push a car that's in neutral, but it does require some effort.
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The point of having the treadmill in this case is to give people a mental hurdle to negotiate in this thought experiment. In truth the treadmill has very little impact on the flight of the plane. A similar question would be "if you paint the plane purple, will it still take off?".
Pushing a car is a bad example because there is a lot more in play than the bearings. If you lift a non-driven wheel up with a jack and release all breaks you will find that you can manually spin the wheel with ease.
Think about it; if wheel bearings had a significant amount of drag (friction), the hundreds of millions of cars and trucks on the road every day would burst into flames due to heat build up.