Forces and Motion

A force is a push or a pull, and forces are behind everything that moves. When you kick a ball, your foot applies a force. When a magnet drags a paper clip across the table, that is a force too. Forces can start motion, stop it, speed it up, slow it down, or change its direction.

Two forces work on you all day long. Gravity pulls everything toward the Earth, which is why dropped things fall and why you stay on the ground. Friction is the rubbing force between two surfaces - it is why your shoes grip the floor and why a sliding ball eventually stops. Ice has so little friction that walking on it becomes an adventure.

Scientists describe motion with speed and direction. A rolling ball has a speed, and if nothing pushes or pulls it, it keeps rolling in a straight line until friction and gravity slow it down. Once you start noticing forces, you see them everywhere: swings, bikes, slides, even pouring juice.