How Sound Gets to Your Ear
- Physics
- Ages 8–11 · Grades 3–5
- Hands-on experiment
What you’ll find out
- Sound is made by something vibrating.
- Sound needs a material to travel through, and cannot cross empty space.
- Pitch and loudness are two different things, changed in two different ways.
No sign-up and no real names. In the lesson you check your understanding as you read, run the experiment yourself, and practise until it sticks.
Something is shaking
Pluck a guitar string and look closely at it. The string becomes a blur, because it is moving very fast, back and forth, dozens or hundreds of times a second. That shaking is called a vibration, and every sound you have ever heard started with something vibrating. Put two fingers on your throat and hum: you can feel it happening. Touch the string with your hand and the sound stops immediately — no shaking, no sound. The vibrating string pushes the air right next to it, that air pushes the air beyond it, and the push travels outwards to your ear.
Sound needs something to travel through
If sound is a push travelling through air, then taking the air away should stop it — and that is exactly what happens. Put a ringing bell inside a glass jar and you can hear it clearly. Now pump the air out of the jar. You can still see the hammer striking the bell, so it is definitely still ringing, but you hear nothing at all. Space has no air, so space is genuinely silent, and every film with a roaring explosion in space has that part wrong. Sound travels through water and wood too, and usually faster than through air.
High or low, quiet or loud
Two different things can change about a sound, and it helps to keep them apart. The first is how high or low it sounds, which is called pitch. A short, tight string vibrates quickly and gives a high note; a long, loose string vibrates slowly and gives a low one. The second is how loud it is, which is about how big the vibration is rather than how fast. A small shake is quiet and a big shake is loud. You can have a high quiet note and a low loud one, so the two are genuinely independent.
Curriculum links: NGSS 4-PS3-2 · NGSS 1-PS4-1