Downhill Race

A red and yellow exhibit table, with an orange and white information panel on top. On the table top sits a purple long wedge contained in clear perspex and has a yellow ball at the high end contained by a steel gate.
A red and yellow exhibit table, with an orange and white information panel on top. On the table top sits a purple long wedge contained in clear perspex and has a yellow ball at the high end contained by a steel gate.

When something spins or rolls, the location of its mass from the central turning point affects how quickly the object spins.

How it works

Have a rolling race between a ring, flat disc and ball to explore rotational inertia. Stand all shapes on their side behind the gate. Raise the gate to start them rolling at the same time.

Things to try or ask around the exhibit

Which shape will win a rolling race—the ring, the disc or the ball?

Background

While each shape has the same size and mass, each one has its mass spread in different areas. This is important for how easily each shape rolls along (‘rotational inertia’). Things need a force (such as a push) to start moving. Heavy things that need a stronger push have more inertia.

Finding the science in your world

Making the rims of racing bike wheels lighter reduces their inertia and makes them easier to turn.

Sometimes, mass is mostly placed on the rim of a wheel, so it will turn with greater force for a longer period of time, such as giant flywheels used in factories.