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Hell Yeah the Plane Takes Off
Thursday, 2008 January 31 - 9:10 am
For fans of and/or Mythbusters, I'm sure you were very interested in last night's Mythbusters episode, where they attempted to answer the old "plane on a conveyor belt" question. I've blogged about it before, but here's the problem again, in case you haven't seen it:
A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?

The answer is, as Kottke put it, "HELL YEAH THE PLANE TAKES OFF". Mythbusters demonstrably proved it, not just with a model airplane on a miniature conveyor, but with a real airplane sitting on a giant sheet of tarp, being pulled by a truck in an opposite direction of the airplane.

As I, and everyone who actually understands this problem, explained before, the reason the plane can take off is that its forward motion is determined by its propeller acting against the air. The wheels on the conveyor provide very little backwards force against the plane; the plane might as well not be touching the ground at all.

Still, legions of commenters (on both and the Mythbusters message boards) refuse to believe it. They claim the experiment was flawed, because the plane moved forward.

The. Plane. Moved. Forward.

Of course the plane moved forward. Nothing in the original problem stated that it wouldn't. That was just the flawed assumption that the problem was designed to exploit. When the problem says "the plane speed", it's talking about the speed of the plane relative to the earth, not the speed at which the wheels are spinning. If the plane remained stationary, the conveyor belt would have to be stationary too, according to the terms of the problem.

Many of the people who are wrong about this don't appear to be stupid. But they just aren't thinking critically. They've formed a flawed mental model of this problem in their heads, and they just can't let that model go. No amount of rational explanation seems to help; any experimental evidence will be met with stubborn explanations of how the experiment was flawed. The scary thing is that eventually, some of these people will be elected to public office, where they will insist that Saddam Hussein was responsible for 9/11, and that's the reason we have to invade Iraq.

Oh wait. That's already happened. Maybe we need a MythBusters episode about that one too.
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