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Originally Posted by Wisha Haddan H3
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.
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Not entirely true.
The plane has to gain distance over time. If the conveyor moves the plane rearward for every instance in time the plane's thrust attempts to move it forward, the net movement relative to the air would amount to zero.
