There is a spot in our school where the classrooms and verandahs make a little tunnel about 10m long. The kids all love the echoey sound and it’s common to see them popping in and out and giggling madly. The little girl noticed it the other day when we were walking through the school and had to stop and investigate.
She was talking as she walked through, and as we got out she stopped and ran back. She tried talking while standing in the middle, then over near one wall, then ran down to another ‘tunnel’ and tried it there. That one has one side only enclosed by a lattice with vines growing through it, so it doesn’t echo. Then she asked the question -
“Mummy! Why does my voice sound funny in there?”
It’s called an echo. When the sound comes out of your mouth it goes forwards and bounces off the wall. Usually the walls are far apart or there are lots of soft things. But in the tunnel there are walls all around and hard.
Think about throwing a ball. If you are outside, the ball goes a long way. If you threw it in a room it might hit some furniture and drop down to the ground. But if you threw it in the tunnel it would keep bouncing off the walls, floor and roof and might even come back and hit you. That’s what is happening with the sound.
Dolphins and bats use echoes to help them see at night or in murky water. They make noises and have very big ears or special bones to pick up the echoes that come back to them, which helps them work out how far away things are.
At least that’s what I would have said, but she ran off half way through to investigate something else. Maybe next time.
Photo courtesy of Kiaura.
Edited: It’s been pointed out below that it wouldn’t be a simple echo, there would be interference between different sound waves. Think of waves bouncing off the edge of a pond and hitting other waves, you end up with splashes. Beats are an example I’ve talked about if you’re interested in how it works, there’s a video with some really nice ones here. The essential point is still the same, that sound bounces off hard surfaces.
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