|2008-02-05 05:35 (UTC)
Now, there is some friction in the bearings, so there is going to be some motive forced on the aircraft, but just a fraction of the full speed.
This is a side point to the main argument, but it's worth explaining because it may help some people understand why the plane does take off:
There was a guy who was studying mining carts. He wanted to know if it was cart speed or cart load weight that made it hard to move mining cars. His name was Robertson, and he came up with something called Robertson's Contrivance.
Basically, it was just a big wheel that had railroad tracks running around the outside. He put an empty mining cart on the wheel, and attached a force measuring gauge to it. Then he ran the wheel at different speeds, measuring the force necessary to keep the cart stationary. Basically he was measuring the force of friction between the cart and the wheel.
He found that there was basically no difference in the amount force necessary to move the wheel at different speeds. It took almost exactly the same amount of force at 5 MPH as 25 MPH.
Then he threw a bunch of rocks and dirt in the mining cart, to make it heavily loaded, and spun the wheel again. It now took a lot more force to make the wheel spin, because the cart was much heavier. But again, no matter what speed he made the wheel go, the new larger amount of force didn't change. It was the same no matter what the speed was.
The conclusion was inescapable: for a vehicle with free-spinning wheels (like mining carts or airplanes) an increase in wheel speed does not result in an increase in friction. The amount of force required to make the cart move depended only on the cart's weight, not on its speed.
This is why ground-speed doesn't matter. The runway can be moving backward at 10x the plane's takeoff speed, but the plane is still going to be able to roll forward. The amount of friction between the plane and the runway does not depend on the plane's speed, only on the plane's weight. And the plane's weight will not increase as it rolls down the runway.