Humming hangers
Sound is made by vibrations. Sound travels better through solids and liquids than through air.
What you need
- wire coat-hanger (available from dry cleaning stores)
- 2 lengths of string, each about 40 cm long
What to do
- Tie one end of a piece of string to the bottom of the coat-hanger and slide it to one side. Do the same for the other piece of string and slide it to the other side.
- Wrap one piece of string around the index finger of each hand so the coat-hanger can swing freely.
- Swing the coat-hanger to make it hit a metal table leg or other metal object (you may ask someone to tap your coat-hanger with a pair of scissors).
Describe the sound you hear.
- With the string still wrapped around your fingers, place your index fingers in your ears and bend over so the coat-hanger doesn’t touch anything.
- Swing the coat-hanger and make it hit the metal object again.
Does it make a different sound?
What's happening?
When we hear a sound, it normally travels through air to reach our ears but sound can also travel through solids and liquids. Solid objects carry sound waves most effectively, then liquids and then gases.
In the first part of the experiment, the coat-hanger hits a metal object and starts vibrating. The vibrations make sound waves that travel through the air to reach the ears and the sound heard is very quiet.
In the second part, the sound waves travel through the string (a solid material) to reach our ears. The sound is much louder because the sound waves travel more easily through the string than through the air.
