Echoes. Sounds That See in the dark.

Echoes. Sounds That See in the dark.

"Hel-l-o-o-o-o-o!"

A boy hears an ecru coming from the hills.

Echo, talk to me', he calls. '...to me', repeats the echo. '...to me...to me...to me.

'What is an echo? It’s a sound you make that bounces back to you from hills or other surfaces. But how can a sound bounce? It's not a ball.

Actually, sound is a wave in the air. If you could see air in the same way as water, you'd see the waves that sounds make. Sound waves bounce only if they hit somethings big and solid like the side of a hill or the walls of a cave.

What if nothing stops t e sound waves? Then they just get smaller and smaller. Or they are absorbed by soft things such as carpets, curtains, or large pieces of furniture. That’s why we don't usually hear echoes in the house.

Do you know that echoes can help some Animals 'see' in the dark?

In pitch-black caves bats fly easily, never bumping into anything, and even eating tiny insects in the air. As they fly they make tiny whistle-like sounds. These sounds bounce back to them. The direction of the echo and the time it takes for it to return tell the bats exactly where things are as they fly.

Human beings have learned to harness echoes for navigation, too. Submarines travelling underwater use sonar to bounce sounds off of solid objects so that they can tell where those objects are located - like undersea bats!