Blinky McSquinty wrote:
I think we're mixing up some scientific facts with some wild misconceptions. Rub your two hands together, feel the resistance. that's friction, period. One result of friction can be heat. keep rubbing your hands together briskly, and they get warm.
Now let's deal with rockets and Newton's third law, which states that for every action there is an equal and opposite reaction
If you and a friend stood on skateboards, and pushed against each other, you would separate and be pushing apart.
Now, if you substitute throwing gas in one direction, the same thing is happening, the rocket is going in one direction, the rocket exhaust is going in the other direction.
What was before the Big Bang? Take two aspirin before you read this..
Most of us think of space as having the three basic dimensions with time as the fourth just marching on. But before the big bang there was no space, no time, nothing, not even three dimensions. Nothing. Not even time.
True, I can only push the other skateboarder because of friction and the concept of thrust is always the same.
Consider the rocket. In a non vacuum, the exhausted molecules hit the atmospheric molecules, creating enough resistance (friction) for thrust.
In a vacuum it's slightly different, but it's still all about friction.
The heated gas expands the exhaust, this tries to return to it's original shape -molecular bindings and cooling effect by it's surroundings-, thereby creating friction (between the gasses and the exhaust).
As the rocket meets no environmental friction, this is enough for thrust.
Where else are the expanding gasses and rocket going to go?
Not unlike a football, it's not the kick that makes the ball travel, the kick dents the ball.
The ball wanting to return to it's natural form (pressure) is the only reason it travels (it can't do so in the same spot, as the foot carries more kinetic energy -try kicking a cannon ball-).
Consider a sailing boat, the wind just 'bends' the sail.
The sail trying to return to it's original shape makes the boat move.
In F1, engine, aero, trannie et all make the tyres try to push the road away, the surface offers enough resistance to force the tyre to move, rather than the track *not intended as an opening for a tyre debate.
Back to OP: yes, motion is possible without friction, acceleration however is not (ignoring gravitatitional pull from other objects).