Ball on a Stick

A pink and orange display table with a vertical blue information panel on top. In front of the panel, are two red cricket balls which each have a shite stick going through them.
A pink and orange display table with a vertical blue information panel on top. In front of the panel, are two red cricket balls which each have a shite stick going through them.

It's easier to control how something moves when the object's mass is far from its turning point.

How it works

Compare whether it's easier to balance a ball on a stick in the air or in the palm of your hand.

Things to try or ask around the exhibit

Is it easier to balance the stick when the ball is in your hand, or up in the air? Try it with your eyes closed or on your fingertip.

Background

If something is sitting still, you need to use a force such as a push or a pull to get it moving. Heavy things need more force to start moving, so they have more inertia. As you try to balance the ball and stick on your hand, it falls and rotates around your hand.

Things that rotate have inertia like other objects. When the ball is up in the air, most of the mass (the ball) is far from your hand (point of rotation). In this position, it has more inertia and rotates more slowly. This gives you more time to use your eye-hand coordination and adjust your hand to save the ball from falling.

Finding the science in your world

Tightrope walkers sometimes hold items in their hands as they move across a tightrope. If their body loses balance, they can 'buy time' to adjust their balance on the tighrope by using the inertia of the handheld item, particularly if they're holding a long beam with balls attached on each end.