Sound and Vibrations

Every single sound is made by something vibrating — shaking back and forth very quickly. When you pluck a guitar string, you can actually see it blur as it vibrates. When you speak, tiny flaps in your throat called vocal cords vibrate to make your voice.

When something vibrates, it pushes the tiny particles in the air next to it. Those particles bump into the next ones, passing the energy along as a sound wave that spreads out in all directions, a bit like ripples spreading across a pond when you drop in a stone.

The highness or lowness of a sound is called its pitch. Faster vibrations make a higher pitch, like a whistle or a bird's tweet. Slower vibrations make a lower pitch, like a big drum or a lion's roar. You can change the pitch of a stretched elastic band by making it tighter or looser.

The loudness of a sound is called its volume, and we measure it in units called decibels (dB). A whisper is about 30 dB, a normal conversation about 60 dB, and a loud rock concert can reach 110 dB or more — loud enough to damage your hearing over time. The bigger the vibration, the louder the sound.

Sound travels at different speeds through different materials. It actually travels faster through solids and liquids than through air, because the particles are closer together and can pass the energy along more quickly. That is a surprise to many people, who assume sound travels best through open air.