Underwater telephone experiment | Fizzics Education


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Underwater telephone

Underwater telephone

Follow FizzicsEd 150 Science Experiments:

You will need:

  • Two plastic funnels
  • Rubber tubing to fit the funnels
  • One balloon
  • A friend in a pool
  • Adult supervision


Underwater telephone science experiment - materials needed
1 Underwater telephone science experiment - cutting the balloon

Fir both ends of the rubber tube with the funnels.

2 Underwater telephone science experiment - balloon stretched over small funnel

Stretch the balloons over the end of one of the funnels, making sure that it is tight across the funnels opening.

3 Underwater telephone science experiment - funnel underwater

Place the funnel, with a balloon, into the pool.

4 Underwater telephone science experiment - holding the telephone

Place the other funnel over your ear. Can you hear sounds from inside the pool? Have a friend talk to you from under the water. Can you hear them clearly?

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6 Teacher showing how to do an experiment outside to a group of kids.

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– Help students learn how science really works

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7 Stylised sound waves on a black background

Get the Unit of Work on Sound here!

  • What is amplitude?
  • What is frequency?
  • How does sound travel and what does it look like and more!

Includes cross-curricular teaching ideas, student quizzes, a sample marking rubric, scope & sequences & more

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Why Does This Happen?

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.

Whales can send and receive messages through water many kilometres away due to the sound being able to travel faster through water than it does in air. Why is this so? Liquid molecules are packed more tightly than the gas molecule. This means that the vibrations travel faster through liquids than they do through the air (and with less energy loss).

Variables to test

More on variables here

  • Is there a limit to the length of hose?
  • What happens if you change the funnel size?
  • Can the underwater telephone work without the balloon?

A man with a glove above a liquid nitrogen vapour cloud

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