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A rocking and rolling demonstration that hits the right groove

## Australian Curriculum links

• Science > Physical Sciences > Year 4 > ACSSU076
• Science > Physical Sciences > Year 7 > ACSSU117
• Science > Physical Sciences > Year 8 > ACSSU155

## You’ll need

• At least seven marbles, all the same size
• A length plastic tube approx 20cm cut in half to form an open pipe

## Try this

1. Place five of the marbles in a row in the middle of the tube, with the tube sitting flat on to of a level surface.
2. Make sure they are all touching each other.
3. Roll another marble down the groove into the lined-up marbles – what happens?
4. Repeat the experiment, and this time roll two marbles into the row of five. Now try with three and then four marbles.

## Further investigation

• What happens if you use marbles of different sizes? Does this change the way the Newton's Cradle behaves?

## What’s happening?

The moving marble has moving, or kinetic energy. The marble you roll collides with the stationary marbles and transfers, or passes on, the energy. This energy is then transferred along the row of marbles with the last marble shooting off.

The number of marbles that you roll towards the stationary ones is the same as the number of marbles that shoot off. When all the collisions occur with objects that are the same size, what goes in should be the same as what comes out.

This is an example of the concept of ‘conservation of energy’ – energy can be transferred from one marble to another, but it does not disappear. Newton’s cradles in which the balls are suspended from string and swing back and forth will eventually stop moving, but this is because during each collision a small amount of kinetic energy is transformed into other types of energy (heat energy, sound energy etc.), reducing the amount of kinetic energy in each collision until the balls eventually stop moving