Blow your own sail
Classical Mechanics
Level
3
The Coyote made a contraption using a sail and a fan to catch the Road Runner. When switched on, the fan blows air, all of which hits the sail.
If the ground is frictionless, what happens when the Coyote turns on the fan?
He stays where he is
He moves forward
He moves backward
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1 solution
Without the sail present, since the fan pushes air molecules forward, for momentum to be conserved the Coyote must move backwards. But with the sail installed, the air molecules that have been blown forward will now bounce off the sail and end up scattering in a general backward direction, (the shape of the sail determining the efficiency of this process, of course). So now, for momentum to be conserved the Coyote will end up moving forward, (as long as the fan/sail setup can generate enough force to overcome any static friction).
Note that if the Coyote were a bit smarter he would ditch the sail and just turn the fan around and blow air backwards, thus propelling him forward, (just like hovercrafts operate). Even that, though, won't be enough for him to catch the Road Runner, because, well, he's the Coyote. :p