Amplitude measures how much something moves or changes from its normal, resting position. Think of a swing at the playground: when you pump your legs just a little, the swing moves back and forth in small arcs close to the center. That's low amplitude. When you pump hard and soar way up high, swinging through big, dramatic arcs, that's high amplitude.

Scientists use amplitude most often when describing waves. Sound waves with high amplitude are loud, while low amplitude sound waves are quiet. The difference between a whisper and a shout is amplitude. Ocean waves with high amplitude are tall and powerful, crashing onto the beach with force. Light waves with high amplitude appear brighter than those with low amplitude.

In earthquakes, amplitude describes how much the ground shakes and moves. A high-amplitude earthquake causes violent shaking that can topple buildings. A low-amplitude earthquake might just rattle dishes.

Amplitude isn't about how fast something moves or how often it repeats. It's about the size or strength of the movement away from the middle point. A guitar string plucked gently vibrates with small amplitude and makes a soft sound. Pluck it hard, and the same string vibrates with large amplitude and rings out loudly.