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11/5/2013 6:38:15 PM
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The Airplane-Treadmill problem.

[quote][i]"Imagine an indestructible 747 is sitting on an indestructible conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?"[/i] [/quote] I still can't decide what the correct answer is to this (if there even is a correct answer). On one hand the engines will push back the air and thus the plane will move forward and take off. But on the other hand the conveyor belt will spin at the same speed as the wheels so that the plane can't move forward. What do you guys think? Will the plane take off or not?

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  • The wheels will move even if the conveyer belt is going, as the wheels are freely spinning. Really, if the plane is held in place, once the engines start up it will move forward and take off normally. The wheels just spin a bit faster, that's all. Remember, planes can take off on water, without propellers for the water.

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    • Edited by Capiton Render: 11/5/2013 7:16:33 PM
      If the plane remains stationary, no it cannot take off, it has to have air passing over the wings. hurr durr

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    • Lift requires air flow on the wings. If the plane is stationary on the belt, it wont take off.

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      • Edited by A Wild Sceptile: 11/5/2013 6:48:33 PM
        [quote] But on the other hand the conveyor belt will spin at the same speed as the wheels so that the plane can't move forward.[/quote]Shouldn't this only matter if the wheels were the driving force of the jet? They spin freely and aren't connected to any sort of drivetrain, so the thrust from the engines should still be able to push the jet forward.

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        • An airplanes wheels don't care if the ground beneath them is moving or not, they aren't what provides propulsion. An airplane will take off from a sufficiently large treadmill

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        • Edited by Catman6: 11/5/2013 7:00:30 PM
          It will take off. The wheels will just spin faster. Since the wheels are essentially 0 friction points, the jets pull in air, moving the plane forwards. Where the OP's question is skewed is the addition of [quote]But on the other hand the conveyor belt will spin at the same speed as the wheels so that the plane can't move forward.[/quote]Sure the conveyor belt will spin to try to keep the plane there, but it will still move. The movement of the plane is independent of the wheels EDIT: I re-read the way the OP was worded. It's not an answerable question because the two speeds don't depend on each other. It will take off, but the wheels and treadmill will end up moving at infinite speed.

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          • No, because they're on the same frame of reference.

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          • Edited by MattyFez: 11/5/2013 6:42:50 PM
            ITT: people don't know modern jet engines suck in air. Still no air flowing over the wings to apply lift.

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          • It won't take off. Flight depends on air moving around the wings.

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          • Answer is no because the treadmill does not move air so the plane remains in the same spot and there is no upward force for the plane to take off...

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