Sound and How We Hear

What is sound?

Sound is a kind of energy you can hear. Every sound starts with a vibration — that means something is shaking very fast, back and forth.

Pluck a rubber band and watch it blur as it wobbles. Tap a drum and feel the skin buzz. That shaking is what makes the sound. Sound is one of the many forms of energy around us.

How sound travels

When something vibrates, it pushes on the tiny bits of air around it. That push makes the next bit of air move, and the next, and the next. The vibration travels outward in sound waves, a bit like ripples spreading on a pond.

Sound can travel through:

• Air — most of the sounds you hear
• Water — that is why you can hear sounds underwater in a pool
• Solids — tap a table and put your ear on it; the sound travels through the wood

But sound cannot travel through empty space. In outer space there is no air to carry the waves, so it is completely silent.

How we hear

Your ears are sound catchers. Here is what happens when a sound reaches you:

1. Sound waves enter your ear.
2. They hit your eardrum, a thin piece of skin, and make it vibrate.
3. Tiny parts inside your ear pass the vibration along.
4. Nerves send a signal to your brain.
5. Your brain decides what the sound is — a bird, a bell, or a friend's voice!

All of this happens in less than a blink.

Loud, quiet, high and low

Sounds can be different in two main ways:

• Volume is how loud or quiet a sound is. Bigger vibrations make louder sounds. A gentle tap is quiet; a hard bang is loud.
• Pitch is how high or low a sound is. Faster vibrations make higher sounds. A tiny bird chirps high; a big drum booms low.

That is why a thin, tight guitar string sounds high, and a thick, loose one sounds low.

Try it yourself! 🎶

Make a simple rubber-band guitar.

1. Find an empty tissue box or a sturdy plastic tub.
2. Stretch a few rubber bands of different thicknesses around the open part.
3. Pluck each band and listen. Watch how it vibrates.
4. Notice that thin, tight bands make higher sounds, and thick, loose bands make lower sounds.
5. Now pluck softly, then harder. The harder pluck makes a louder sound because the band vibrates more.

Bonus: Gently rest your fingers on your throat and hum. Can you feel the vibrations? Those are your vocal cords making sound!

Stay safe: Never put anything into your ear, and keep very loud sounds away from your ears to protect your hearing.