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Originally Posted by PARAGON
That really has nothing to do with it.
Wheels have to turn in either situation. In the case of the plane, it has to move relative to air to lift off, a car doesn't. That is the only difference. How they apply their power has no bearing on this riddle.
Even if a plane is "pushing the air" it has to push against that air (thrust) to make the plane move, gaining speed. As it gains that speed the conveyor is matching the speed in the opposite direction, same as a car would.
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Somehow missed this post. On the contrary, how airplanes apply their power is
central to this riddle.
For example, when we walk or run, our propulsion is based on applying force to the ground. We push backwards and resistance sends us forward relative to the ground and air. On a treadmill, our feet push the conveyor belt and all our walking force is spent keeping up with it. We feel no wind in our face because our speed (relative to the ground and air) is zero. A car, bicycle or any vehicle that uses ground propulsion would experience the same effects on a conveyor belt.
However, an airplane's engines don't push the ground. They apply force directly to the air. When the air pushes back, the plane is thrust forward through the atmosphere at ground level. The wing's movement through the surrounding static air creates lift and the plane takes off.
On a conveyor belt runway, the exact same process occurs ... the engines push air backwards and the plane is thrust forward through the atmosphere. The conveyor belt can spin all it wants to, but it will only make the wheels spin faster. It can't hold the plane back because it isn't attached to the plane. Since the plane thrusts directly on the air, it doesn't rely on the conveyor belt for propulsion the way a person or car would. Instead, it slices through the air and takes off when enough lift is achieved.