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Investigative Rain Stick

A twisted piece of aluminium foil in the shape of a corkscrew coming out of the end of a piece of 20mm pvc pipe.

Love the sound of the rain, but hate getting wet? With this home-made musical instrument you can make the sound of the rain yourself; no water required!

Australian Curriculum links

  • Science > Physical Sciences > 1 > ACSSU020
  • Science > Science as a Human Endeavour > 1 > ACSHE022
  • Science > Physical Sciences > 4 > ACSSU076

You'll need

  • scissors
  • ruler
  • aluminium foil
  • permanent marker
  • 3 long cardboard tubes (e.g. the inside of an aluminium foil roll)
  • sticky tape
  • ¼ cup dry uncooked rice
  • ¼ cup sesame seeds
  • ¼ cup dry uncooked lentils

Try this

  1. Cut a 60 x 30 cm piece of aluminium foil and loosely scrunch it lengthways, to make a 60 cm long, cigar shaped, foil snake.
  2. Coil the snake of foil around the permanent marker to form a tight spiral shape (like a slinky).
  3. Insert the foil spiral into a cardboard tube and tape each end to the inside of the tube.
  4. Cut a piece of aluminium foil large enough to cover one of the open ends of the tube. Tape it over one end of the tube to form a tight seal.
  5. Pour the rice into the tube through the open end.
  6. Repeat step 4 for the other end of the tube and label the tube “Rice”.
  7. Tip the tube upside down and listen to the sound it makes.
  8. Repeat steps 1 to 7, replacing the rice with the sesame seeds or lentils, to make 3 different rain sticks. How do the sounds made by each filling differ?

Further investigation

Try using only one type of filling, but instead using a longer tube (like one from a roll of wrapping paper). Does the sound change? Try using a longer or shorter piece of aluminium foil. Does that make a difference? Instead of using a foil spiral, try pushing toothpicks through the cardboard tube in a spiral pattern (you might prefer to use a toilet roll for this as the cardboard is thinner). Which of these physical changes affect the vibrations (and therefore the sound)?

What's happening?

When you tip the tube, the rice, seeds or lentils fall downwards and bumps (or 'collides' with) the aluminium foil spiral. Each collision starts a vibration that we then hear as a soft tapping sound. Each particle makes a series of tapping sounds as it continues to fall down the tube and collide with the foil. When lots of particles fall at once, they make a repetitive sound a bit like the rain. The sound only stops once all the particles have stopped falling.

You may notice that the three rain sticks make different sounds. This means that the vibrations that made each sound must also be different. If the vibrations are faster, the sound they make have a higher pitch. If the vibrations are slower, the sound they make have a lower pitch. The vibrations are different in each rain stick because the fillings are made of different types of particles (grains of rice, sesame seeds, and lentils). Differences in the size, composition and weight of each particle can affect the speed of the vibrations during the collision.

Real world links

A rain stick is a 'percussion instrument', which is an instrument that produces sound by striking or scraping. A rain stick is a particular type of percussion instrument called a 'shaken idiophone'. This means the person playing the instrument does not directly strike it themselves. Instead they do an action which causes something else to do the striking and produce the sound. In the case of the rain stick, the performer turns the instrument upside down, which makes the rice grains fall and strike the foil spiral.