Okay, so this is either really complicated, or really simple. I had this theory about something, that I've never been able to fully test. As a kid, I used to love to sit on a skateboard or a wheeled computer chair and lean to one side, then quickly slide my feet (and the board/chair) underneath me to the other side, then repeat again and again, to move across the floor without touching anything. Now, I had a thought recently that perhaps this is a trick on conservation of momentum, which allows an object to create an imbalanced force, and therefore move, using only sources of momentum within its own mass, via a clever manipulation of inertia. However, I couldn't be sure if air friction had anything to do with it or even the rolling friction from the wheels, or well... any kind of friction. I'd basically need to go to space to confirm that theory, so I thought I'd ask some physicists, or at least someone keen on the general concepts of physics like myself. Basically, here's the question. If you had a short, high acceleration in one direction, balanced by a long, low acceleration in the other direction, both acting on the same mass, would they cancel each other out, or create a net imbalance? I know that F=MA, but I don't know how that translates to acceleration over varying lengths of time versus varying acceleration rates. any physics majors/geniuses out there who can help me out? This is purely for curiosity reasons.