Did you know that sound is a wave? Not like a wave you’d ride on a surfboard, but similar. Sound is a wave that travels through the air. It starts from a vibrating thing, like a plucked guitar string or a ringing bell. The vibrating thing moves the air around it back and forth, sending out waves in the air like ripples on a pond. When those waves hit your ear, you hear them as sound!
Sound waves can hit other things too. They have energy, and just like ocean waves crashing against a cliff, they give that energy to things they hit. When sound waves hit the thin bottom of a paper cup, for instance, they make it vibrate. And if that paper cup is connected to a string, then the vibrating of the cup makes the string vibrate too. And if that string is connected to another paper cup, then that paper cup will also vibrate. That means you can hear the sound from one paper cup to another!
So weirdly, even though sound is a wave in air, it can travel through other things too — as long as they can carry its vibrations. Try transferring sound with this phone-tastic project!
Gather your materials.
Poke a hole in the middle of the bottom of each cup. The hole should be large enough to thread the string through.
Cut a piece of string at least 5 inches long. Then, pull either end of the string through the bottom of each cup.
Tie a paper clip to each end of the string. The paper clips will keep the string from pulling out of the cups.
Hand a friend one of the cups. While you hold the other, walk away from your friend. Stop walking when the string is tight!
Have your friend place their cup over one of their ears while you speak into your cup. Can they hear you?
Alexander Graham Bell, the inventor of the first practical telephone, based his design on similar ideas to this string cup telephone. The telephone has a microphone that gets energy from sound waves spoken into it, and a speaker that vibrates to make the sound you hear. Instead of using a string to transmit the sound, though, the telephone uses electricity!
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