Year 4 Science

science owl

Sound and Hearing

Good Vibrations

An alarm clock rings, a dog barks, a voice calls: 'Time to get up.' Every day is full of familiar sounds. But what exactly is sound? Sound is caused by a back-and-forth movement called vibration. Try this. Close your lips and hum. While you're humming, feel your throat under your chin. Do you feel a tingling? It is caused by something moving back and forth very fast. When you hum, the vocal cords in your throat are vibrating back and forth, which makes the air around them vibrate. These vibrations of air strike your eardrums and make them vibrate, to create the sound you hear.

sound vibration dog

Here's a way you can see how sound makes the air vibrate. Stretch a piece of cling film over the surface of a bowl and fasten it tightly with a rubber band. Sprinkle a few grains of dry rice, salt or sugar on the film. Now take a big pan, hold it near the bowl and strike it with a spoon a few times. Do you see the grains jump when you hit the pan? That is because the pan is vibrating, which causes the air and then the plastic to vibrate. We call the vibrating air sound waves. When you hit the pan, sound waves travel through the air and cause the plastic to vibrate, which in turn makes the grains jump.

Sound waves move out from a vibrating object in all directions, making the air move back and forth in a way that we can't see. Sounds compress and decompress the air, pushing and then relaxing, making invisible vibrations. Those back-and-forth vibrations spread out from the source that made them, getting weaker as they get farther away. That's why you hear your friend standing right next to you more clearly than you hear someone calling from across the street.

This activity is adapted from page 322 of What Your Year 4 Child Needs to Know, which can be purchased here. Click below to see the related activities.

science owl
science owl