Newton's First Law of Motion
Newton's First Law of Motion tells us that
An object in motion tends to remain in motion, and an object at rest tends to remain at rest.
If you were out in space and you gave a rock a push, its momentum would keep the rock moving at the same speed in the same direction until it bumped into something. On the other hand, if you put a rock in space and left it there not moving, its inertia would keep it right there, hanging in space, forever (or until something bumped into it or it came under gravitational or magnetic pull).
On Earth, objects don't really remain in motion, because friction slows them down, and gravity pulls them toward the ground.
To find out more about movement, check out these books from Amazon.com or from your library:
