Talking about force, I wonder if a rocket could fly across a vacumn, which does not have anything at all. I just wonder how could force produce motion if there's no friction for it to force a motion.
It could indeed, and they do so on a regular basis. A rocket's action should not be compared to that of tires on a road, where an icy road will prevent the vehicle from moving forward. Instead, the rocket moves because it throws gas molecules out of its exhaust nozzle. These molecules have significant mass. Thus when the rocket pushes against the gas in the process of expelling it, the rocket is also pushed forward.
Put on a pair of roller skates, pick up a small, heavy object, and throw it. The air friction on the thrown object will be negligible, but you'll be propelled in the opposite direction nonetheless.
As long as there's something to throw and a means of propelling it out of the nozzle, the rocket will continue to accelerate.
Is outer space a vacumn?
Yup. A much better vacuum than we can produce on earth, in fact. You don't have to go all that high to find it, either. A few thousand miles will do it, I think. Communication satellites operate in such conditions.
M Kinsler
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