A tin or plastic can telephone is a type of acoustic (non-electrical) speech-transmitting device made up of two tins, paper cup, plastic cups or similarly shaped items attached to either end of a taut string or wire.
It is a form of mechanical telephony, where the sound is converted into and then conveyed by vibrations along with a string liquid or solid medium, and then reconverted back sound.
Before the invention of the electromagnetic telephone, there were mechanical acoustic devices for transmitting spoken words and music over a distance greater than that of normal speech. The very earliest mechanical telephones were based on sound transmission through pipes or other physical media, and among the very earliest experiments were those conducted by the British physicist.
Today, we are teaching the kids steps of making a mechanical telephone.
Get a piece of string and two empty cans. If you don't have cans or you don't want to work with them, you can also use cups (preferably plastic), such as the one my kids used. Plastic is a little easier to work than metal. Styrofoam cups do not work well because they are soft and spongy and absorb sound instead of transmitting it. In a pinch, you can use disposable paper cups, but plastic and metal take more wear-and-tear.
Punch a hole at the bottom of each can just small enough for the string to fit through. You might need your parents or teacher to help with this. I helped my kids to get the hole done. You can make the holes with a drill, hammer, and a nail, or other sharp, pointed tool. If you are using plastic cups, you can probably just poke a hole with a push pin or any other sharp point. Make sure the holes only large enough to put the string through and not larger.
Pass the string through the hole and into the bottom of the can or cup. It might help to push the string through with the end of a paper clip or thread it through with a bit of wire.
Tie a knot at the end of the string that is inside the cup.
Place the untied end of the string through the bottom of the other can or cup.
Get a partner
Place the open end of one can over your ear and have your partner speak into the open end of the other can. Make the string as tight as you. If you have made it correctly, you should hear your fiend speak, even if it a long piece of string. Then, talk while your friend listens.
Even in the era of the cordless and the mobile, there's a lot to be said for the old-fashioned tin-can phone. There's nothing flashy about this model, and we can't send email through the wire-er, string. But it offers something more modern versions don't-a fun project to make with a friend, and a dramatic illustration of vibration and waves.
Let me know your thought on this at the comment section!