? Library of Wonders   The Wonder of Sound

Why can you hear through a string telephone?
Connect the bottoms of two paper cups with a string, and, ta-da, you have built a string telephone! If you talk into one of the paper cups, your voice will reach the other paper cup. How does this work?

We saw before that sound is carried, or transmitted, by air to your ears. But, in fact, many materials other than air can transmit sound. With a string telephone, it’s the string that transmits the sound. What’s interesting is that string, being a solid, transmits sound better than air, which is a gas. The reason is sound travelling through air gets weaker and weaker. But sound travelling through a solid material is transmitted without getting weaker. One tip for a better string telephone is to keep the string taut. With the string tight between the cups, the transmitted sound will be stronger. But if you pinch the string in the middle, it will stop transmitting sound.