Diff with a Difference

Simple machines work together to steer a car.

How it works

Turn a handle and observe how separate gears and axles turn car wheels at different speeds. Try holding one wheel still and keep turning the handle to observe how the second wheel responds.

Things to try or ask around the exhibit

• How do the wheels spin differently?
• Why do the wheels need to at different speeds as you drive around a corner?

Background

Each wheel has a separate axle and they are linked together by a set of bevelled, differential gears. When you hold one wheel still (or when the car goes around a bend), the two smaller gears (planet pinions) within the differential are forced to roll around the slow moving, larger inner gear (the sun gear) without turning it. This allows the wheels to turn at different speeds.

Finding the science in your world

As a car drives around a bend, the wheel on the outside of the bend travels further and faster than the wheel going around the inside bend. The differential gears let each wheel travel at different speeds, so the car stays in control as it travels around a bend.