You can hear if someone talks to you from the other end of a room. But if the room is pretty huge, and the other person’s talk is close to a whisper, then? It is doubtful. Let us find a way to make sound waves travel more effectively. Of course, this is what telephones do. There was a time when there were no telephones to connect us with the world. Today we will make our own telephone with a few simple things that we can easily find at home. This string telephone science project is the easiest way to demonstrate the transmission of sound waves.
What we need
Paper or plastic cups – 2
Cotton string – 20 to 30 feet long
Paper clips – 2
Sharp pencil/ Needle – 1
You need a companion too
Procedure
- Punch a small hole at the bottom of each cup.
- Insert either ends of the string through the holes in the cups. The string should be inserted from below.
- Attach a paper clip to the loose end of the string inside the cup. This is to make sure that the string does not slip out from the cup.
- Now we have the two cups connected through a string, and with their mouths pointed in opposite directions.
- Hold one cup in your hand. Ask your companion to hold the next cup.
- Keep moving farther from each other while holding the cup in your hands.
- Stop when you find that the string is tight and can no longer be pulled.
- Now you will be 20 to 30 feet away from your companion.
- Ask your companion to talk into his cup while you keep your ear to your cup.
- Make sure that the talk is above a whisper, but not too loud. Can you hear the talk?
- Now ask your companion to talk without the cup, while keeping the voice at the same level. Can you hear him now?
- Now we are moving to the last part of the string telephone science project. Move a little closer to each other and let the string go slack.
- Try talking and listening through the cup. Is the phone effective when the string is not tightly held?
Explanation
Why are we able to hear through the cup a voice that would not be otherwise audible? When we talk, the sound waves create vibrations in the air inside the cup. These vibrations are passed through the bottom of the cup to the strings. The vibrations travel along the string and reach the second cup where they are again converted into sound waves. This is how you were able to listen to the voice of your companion.
Why are we able to hear the sound with the cup, but not without it? Although sound waves can travel through air, it can travel more efficiently through solid and liquid mediums. This is because the density of solids and liquids is more than that of air. So the sound which was less effectively transmitted through air becomes audible when transmitted through string.
What will happen if the string is allowed to go slack? The vibrations caused by sound waves will just stretch the string, and it won’t cause vibrations in the second cup. Sound waves will reach the cup at the other end only when the string is taut and fully stretched. Now get one more person to hold the string in the middle while you try to listen to the voice from the other side. Note down your observations.
Are you are looking for more such easy-to-do projects? Head to our Projects section, and you will find a lot more.
Here’s Something You Might Like
As a participant in the Amazon Associates Program, Science4Kids may earn from qualifying purchases.
