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Harmonies in Your Head: Make Amazing Sounds Only You Can Hear

Learn how sound travels by making secret sounds with a friend


Can you hear the vibration? Learn about how sound travels in this super subtle activity.
George Retseck

Key Concepts
Physics
Sound
Perception
Vibration
Pitch
 
Introduction
Making music can be a lot of fun—and it is also a great way to explore the physics of sound. With some string and a friend even an absolute beginner can play a nice tune. This experiment is especially interesting because what is audible to you can barely be heard by anyone else.
 
Background
You hear sounds when vibrations get inside your ear and stimulate your nerves to send electrical signals to your brain.
 
Sound waves carry vibrations into your ears. Inside your ear moving air pushes on your eardrum and starts it vibrating. Your eardrum, in turn, pushes on the bones of your middle ear, the tiniest bones in your body. These bones act like a set of levers, pushing against the thin membrane that covers the opening to your inner ear.
 
Materials

  • A helper
  • A piece of string about five feet long
 
Preparation
  • Put your hands over your ears.
  • Have your helper loop the string around your head and over your hands and gently pull the string.
 
Procedure
  • While pulling gently, have your helper pluck the string. What do you hear? Why do you think that is? What can your helper hear?
  • Have your assistant pull the string tighter. What do you hear? Has the sound changed? Why do you think that is?
  • Now have your helper slightly loosen the string. What is different about the sounds now? Why might that be?
  • Now let your helper take a turn listening. This time you pluck the string that's looped around your helper's head. What do you hear? Ask your helper what he or she hears.
  • Change the tension on the string and ask your helper to describe what he or she hears.
  • Extra: Try the same activity with different sizes or types of string (such as nylon string, cotton string or shoelaces). How does the size or type of material seem to affect how well the string transmits waves as sound? What about the pitch?

 

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