Sounds can be high or low. But they can also be loud or soft. What makes a sound loud or soft?
Sounds are the vibrations, or back-and-forth movements, made by moving objects. Strong vibrations make strong sounds. Vibrations are strong when an object moves a lot.
You can make a sound by stretching a thick rubber band and then plucking it with your fingers. If you pluck the rubber band hard, the back-and-forth movements are bigger. Bigger movements make a louder sound. If you pluck the rubber band lightly, the back-and-forth movements are smaller. So the sound is softer.
Scientists measure the strength of a sound in units called decibels. A sound of zero decibels is the weakest sound a person with normal hearing can hear. A sound of 140 decibels hurts your ears.
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