Forces and Motion Together

Remember: a force is a push or pull. Forces are what change motion! A ball sitting on the ground will not move until a force acts on it — like your foot kicking it. Once the ball is rolling, it will keep rolling until another force stops it — like friction or hitting a wall. This idea was figured out by a scientist named Isaac Newton over 300 years ago. He said: things at rest stay at rest, and things in motion stay in motion, unless a force acts on them!