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Ear gongs

 
 

Overview

Materials list

  • 1 coat hanger and other metal objects, e.g. cutlery
  • 1 metre of string or thread
  • A hard surface to bang it against, e.g. a desk

Practicalities

As you are asking students to put their string-wrapped fingers in their ears it may be wise to warn them against pushing them too far in or sticking other objects into their ears.

Discussion

  • What does it sound like before you put the string in your ears compared with after? Why?
  • Where is the sound coming from? How can we hear it?
  • Why do we need the string? What would happen if you try to put the hanger directly against your ear (don't try with any sharp bits!).

Extensions

  • Try different types of string or thread.
  • Try with different objects made of metal and other materials.
  • What happens if every member of the group ties a piece of string onto the object? Does the sound get louder, softer or stay the same? Can everyone hear it?
  • What if your friend ties a thread onto one of your strings? Will he/she be able to hear the sound too? Can you still hear it? How has the vibration travelled?
  • Bring in a triangle from the school's music room. When this is struck it makes a clear sound that we can hear through the air. Why do we need to hold it by the string?
  • What does it sound like if we hold the metal directly? How is that relevant to the coat hanger experiment?

Links to everyday life

If a wooden telegraph pole or railway sleeper in good condition is tapped with a hammer, it produces a clear, crisp sound. If the wood is rotten, the sound will be more of a dull thud. This technique is used to help ensure that railway lines and telegraph poles are safe, either as routine maintenance or after a natural disaster such as an earthquake.

Look out for new mobile phone and music headphone designs that allow you to listen to sounds through your skull. The phone or headphone touches your cheek or just behind your ear and sound vibrations are carried through the bones in your skull to the small bones in your inner ear without the sound going through your ear. This technology is also used by the military, whose helmets allow the user to hear normally but make almost no sound.