Equipment List
- Two metal spoons
- 120cm (approx. 48 inches) string
Instructions
- Fold the string in half to find the middle.
- Tie the middle of the string around the top handle of one of the metal spoons and secure with a knot.
- Wrap one end of the string around one of your index fingers, and the other end around your other index finger, so that the spoon dangles in the middle.
- Ask somebody to tap the hanging spoon with another metal spoon. Listen to the sound produced.
- Put your fingers holding the string against each ear, as if you are plugging your ears from noise, making sure the spoon is hanging at your waist.
- Ask somebody to gently tap the hanging metal spoon with another metal spoon. Listen to the sound coming through the string. Does it sound different?
Why does the sound change?
When the two spoons hit each other they vibrate, creating sound waves. These sound waves travel both through the air and directly along the string to your ears. Because sound vibrations travel better through a solid than through the air, the waves produced by the vibrating spoon, which travel up the string to your ears, are much easier to hear than the waves which reach your ears by passing through the air.
The sound that you hear will change depending on the size of the metal spoon used. Different sized spoons create different wavelengths of sound due to the atoms that make up the spoons vibrating differently. The volume of the sound will also change depending on how hard the spoon is tapped. The harder it is hit, the bigger the amplitude or size of the sound wave that is created, and so the louder the volume of sound.
Changing the length of the string between the spoon and your ears will also change the sound you hear. The faster an object vibrates, the higher the pitch of the sound. Shorter string lengths vibrate more quickly than longer string lengths, so the spoon noise will have a higher pitch as you shorten the length of the string, and a lower pitch when you lengthen it.
Investigate Further
What happens to the sound when you use a wooden spoon to tap the metal spoon? Or two wooden spoons? Why do you think the spoon material changes the sound?
Shorten the string by wrapping it around your fingers more and listen to the sound produced from tapping two spoons. Does it sound different Why do you think this is?
Is the sound the same if you use a metal fork instead of a metal spoon
Have fun using the science of sound to pass on 'secret' messages. Attach a plastic cup to each end of the string. Keeping the string taut, listen with the cup to your ear as someone else speaks quietly into the other cup.
