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Underwater telephone experiment

You will need:

  • 2 Plastic Funnels
  • Rubber tubing to fit the funnel
  • 1 Balloon
  • A friend in a pool!
  • NB: Supervise the balloon with young children



  1. Fit both funnels into the ends of the rubber tubing.
  2. Stretch the balloon over the end of one funnel - make sure it's tight across the funnel
  3. Place the funnel with the balloon into the water.
  4. Place the other funnel over your ear - can you hear sounds from underwater?
  5. Have a friend talk to you underwater - can you hear them clearly?
underwater telephone

What is going on?

Sound is produced by vibrations. The stretched balloon picks up vibrations travelling through the water. As the balloon starts to vibrate it amplifies the sound so you can hear it.

Whales can send and receive messages through water many kilometers away due to sound being able to travel faster through water than normal air. Why is this so? Water molecules are packed more tightly than the gas molecules in air, causing vibrations travel to faster through liquids with less energy loss than they do through gases.

For more on the science of sound check out the external link at the Canada Science and Technology Museum.

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