Orbiting Money

Why sing for your money when you can make your money sing for you?

Australian Curriculum links

  • Science > Physical Sciences > Year 1 > ACSSU020

You'll need

  • 30 cm balloon
  • 50 cent coin (or a hex nut)
  • balloon pump (optional)

Try this

  1. Place the coin inside the balloon by pushing it in through the neck of the balloon.
  2. Use the balloon pump or your breath to inflate the balloon and tie the balloon off.
  3. Hold the balloon with one hand and swirl it around in a circular motion until the coin runs around the inside of the balloon, rolling on its edge.
  4. Observe the coin's motion and listen to the sounds being produced.

Further investigation

Find out what happens if you use a 5-cent coin. Is the sound different? Why?

What's happening?

The shape of an Australian 50 cent coin is dodecagonal. This means a 50-cent coin has twelve sides and corners. As the coin orbits, it rolls on its twelve-sided edge along the inside of the balloon. Vibrations are created when the corners of the coin run along inside of the balloon. A vibration is simply something moving backwards and forwards. All sounds start with vibrations.

In this activity, when the corners of the coin run along the inside of the balloon, the balloon vibrates, and that vibration produces a sound. Fast vibrations result in high sounds and slower vibrations give lower sounds. A faster orbiting coin makes the balloon vibrate more quickly and the pitch becomes higher. A slower orbiting coin makes the balloon vibrate more slowly and the pitch becomes slower.

Real world links

The Australian Mint creates coins in different shapes and sizes in order to assist visually-impaired people with recognising the coins by touch and feel. The original 50 cent coin was introduced in 1966. It was circular in shape and made mostly of silver. In 1969 the coin was changed to a dodecagonal shape and to a composition of mostly copper because silver prices rose and people found it difficult to distinguish the 50 cent coin from the circular 20 cent coin. For more information about Australian currency, visit the Australian Mint website.