Balancing Balls

A rectangular blue and clear perspex shape sitting on edge that has two silver balls inside.
A blue and purple exhibit table with an orange, purple, and white information panel on top of it, sits in front of two green and blue walls. On the table is a rectangular blue and clear perspex shape sitting on edge that has two silver balls inside.

Puzzles can be solved using forces of physics.

How it works

Try to perch two loose balls inside an enclosed container onto separate ledges, without touching the balls.

Things to try or ask around the exhibit

Can you balance one ball on each ledge at the same time?

Background

If you swing a ball on a piece of string around your head, the ball goes round in a circle. If you let go of the string, there is no longer any force on the ball to make it go round in a circle. Inertia causes the ball to fly off at a tangent; the actual direction the ball was moving when you let go, due to centrifugal force.

As you start to spin the enclosed container, friction causes the balls to start moving away from the centre, as well as around in a circle, so they spiral outwards. Inertia keeps them travelling outwards until they come to the outside casing. This then pushes on the balls and they go around in a circle.

Finding the science in your world

Wet clothes spin around inside a dryer's barrel until water is ejected from the clothes (and the barrel's holes) due to centrifugal force.

Chemists and biologists also use a centrifuge machine to separate substances in a mixture.