Echo

sound · physics · acoustics

Sound bounces back. When sound travels through the air and hits a surface like a mountain or a wall, it bounces off and comes back to you as an echo. That's why you hear the same sound twice.

Delay tells the distance. The longer you wait to hear the echo, the farther away the reflecting surface is. A distant cliff makes you wait longer for the echo than a nearby wall does.

Wells are echo chambers. A deep well is a perfect place to hear an echo because sound travels down, bounces off the water or bottom, and bounces back up to your ears with a noticeable delay.

Needs space and surfaces. You can't hear a good echo in a tiny room with soft furniture because the sound gets absorbed instead of bouncing back clearly. Empty, hard-walled spaces work best.

Bats use echoes to hunt. Bats make clicking sounds and listen to the echoes bouncing off insects in the dark. This helps them find and catch their food without needing to see.