2 paper cups
A sharp pencil
String (20 feet or longer)
Take the 2 cups and invert them. Take the pencil and mark the centre for both the cups.
Using the pencil, poke a hole through the marking. It must be kept in mind that the hole should be big enough for the string to pass through.
Thread one end of the string through the hole and into one of the cups. Tie a knot to hold the string inside the cup.
Repeat the same for the other end of the string and tie a knot inside the other cup.
Hold one of the cups and pass the other one to a friend. Walk away from each other so that the string attached becomes tight.
Ask your friend to hold the cup over his or her ear as you speak into your cup. Or hold the cup to your ear and ask your friend to speak. Observe what happens.
How does it work?
The person holding the cup to his/her ear will be able to hear whatever is being spoken into the cup. Sound is produced when things vibrate (move back and forth or up and down). When a person speaks into the cup, the string acts as a medium to transfer sound. The vibrating air enters the ear of the listener, causing the eardrum to vibrate.
The string must be pulled tight for this experiment to work. If the string is loose, the vibrations may not work effectively, and the listener may not be able to hear anything. Also, allowing the string to come into contact with any other object will weaken the signal on the receiving end.