carpal tunnel
Registered: 13/07/2000
Posts: 4180
Loc: Cambridge, England
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Quote: The problem is really a lot simpler than what we've made it out to be in this thread. Its only goal was to make you go "Oh, duh, right, the propeller thrusts against the air, not the ground."
It's a bit more subtle than that; it's also asking "Does the force due to friction increase with speed?". If yes, then there's a belt speed at which the thrust is balanced-out, and the plane doesn't take off. If no, the plane takes off.
And in fact the answer is that friction doesn't increase with speed, but that's a slightly surprising fact, and plenty of people's "folk" understanding of physics won't encompass it.
Peter
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