Science Snack
Learn a little string theory.
Learn a little string theory.

Wrap a string around your head and pluck it to play music.

Tools and Materials

A piece of string at least 3 feet (1 meter) long

Assembly

None needed.

To Do and Notice

Place the middle of the string behind your head, pull the string across your ears, and hold the two free ends together in front of your face. The string should cross over the opening in each ear. Pluck the string, and listen to the tone it makes.

You can hear your string, but the sounds are so quiet you will not disturb other people even if they are close to you.

How can you change the sound? Pull the string tighter, or make it looser, and listen to the change in pitch. Change the length of the string by sliding your hand along the string while keeping the tension as constant as possible. Then listen to the change in pitch.

What’s Going On?

In this activity, you can actually hear how a string’s frequency of vibration depends on its tension and length. When you pull the string tighter, you increase the tension in the string, so the pitch of the sound you hear increases. When you keep the tension constant and decrease the length of the string, the pitch also increases.

You’re hearing the resonant frequencies of the string. The frequency is inversely proportional to the length of the string, and proportional to the square root of the tension in the string. The different pitches you hear are produced by the different frequencies of the vibrating string. High-pitched sounds are produced by higher frequency vibrations, and low-pitched sounds are produced by lower frequencies.

Going Further

Many city bus services do not allow people to play loud music on buses. We find that if you wrap a string around your head and play music, not only will you abide by city laws, but you’ll find yourself with more room as others move away from you.