Science of the Spin Pass

Have you ever wondered why rugby players spin the ball when they pass it between each other? Here is a little bit of science to help explain…

Why do you spin a rugby ball?

The shape of the ball* is obviously a really important part of rugby. One problem with the oval shape is that when you throw it through the air, any wobble that it has makes a lot of drag, a force that slows down the ball and makes its direction unpredictable. If you watch a good rugby player throw a ball, you will see that they twist their hand as they throw. This twist makes the ball spin like a corkscrew as it flies through the air. The idea of the spin pass is to stop the ball wobbling so that the ball can travel a lot further and in a more predictable direction!

But why does the spin make the ball more stable in the air?

If you've ever been on a bike you will have noticed that it is difficult to stay upright when the bike is going slowly but as you go faster you are much more stable. This is because of something called the gyroscope effect. The spinning of the bike wheels creates a force that makes the bike less likely to fall over. You may have seen small gyroscope toys that can balance on your finger or on a tiny point for as long as they keep spinning but when they slow down they fall over.

The spinning of the rugby ball does the same thing. The gyroscope force created when you spin the ball keeps the ball lined up in the same direction as it flies through the air, and with less wobbling you get less drag, so the ball has more chance of making it into the safe hands of your team mate.

Someone has even developed a ball that is half round and half oval shaped so you can practice your spin throw against a wall!