Particle accelerator

A ball in a plastic bowl or a coin in a balloon can teach you some of the physics of a particle accelerator.



Place the coin inside the balloon then inflate and seal the balloon.

To do and Notice

Hold the balloon in your hands.

Move the balloon in a small horizontal circle.

When the coin starts rolling around inside the balloon try to find the timing to add energy to the coin.

When you find the right timing, the coin will speed up each time it goes around the accelerator reaching a high rate of speed.

The coin will also climb up the wall of the balloon approaching the equator as it reaches high speeds.

Once the coin is moving fast hold the balloon still.

Feel the coin as it runs over your finger tips inside the balloon.

Notice the coin slow down as it slowly drops back down to the bottom of the balloon. the rubbery surface of the balloon is removing energy from the coin producing a decelerator.

You can decelerate the coin even more quickly by moving the balloon in small circles in the opposite direction, you must still get the timing of your circles right.

What's Going On?

The timing of your small circles has to be just right to accelerate the coin.

Accelerator physicists must time their pushes on the accelerating particles just right to get them to accelerate to the highest energies.

Going Further

Put two coins in a balloon.

The coins may start out separate, but they will eventually merge together into one pair of coins moving around together.

The coins clump together, just as particles are focussed into beams and gathered into pulses by forces in the accelerator.

Can you figure out what causes the coins to come together.



Scientific Explorations with Paul Doherty

© 2000

8 November 2000


Consider the forces on two bowling balls resting on a trampoline, what causes them to come together?

Consider the forces on two people in a soft bed?

The coins rolling on the elastic surface of the balloon are like the bowling balls on the trampoline.


Each rolling coin makes a depression in the elastic membrane of the balloon and the other coin falls into the depression.