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Moving in space is tricky because of Newton's third law: every action has an equal and opposite reaction. On earth, we don't tend to notice this as much because many other forces (like gravity and drag, or air resistance) stop us.

But in space, everytime you move one way, an opposite motion is created! Throw a ball forward, and you fly back! There is nothing to stop you from experiencing the opposite reaction.

This is why astronauts use many hand holds to move through their stations and ofhen tether themselves to a spot to work.