Spin makes air flow faster past one side of the ball than the other. Faster air means lower pressure, so the ball is pushed from high to low pressure. Pick a spin and hit.
Model: real ball masses and sizes. Weight, air resistance and the Magnus force are recalculated 500 times per second of flight.
This is the diagram AQA asks you to draw. It updates with the spin you choose. The side of the ball rotating into the oncoming airflow slows the air down, so pressure there is higher. The Magnus force acts from that side towards the low-pressure side.
Side-on for topspin and backspin. From above for hook, slice and a curling free kick.
The one rule that gets every diagram right. Find the surface of the ball that is rotating into the oncoming airflow. The air there is slowed, so pressure is high. The opposite surface moves with the airflow, so the air is faster and pressure is low. The Magnus force acts from high to low.
Topspin and backspin happen about a horizontal axis, so draw them side-on. Hook, slice and a curling free kick spin about a vertical axis, so draw them as if looking down from above.
| Spin | Eccentric force | Slower air · high pressure | Faster air · low pressure | Magnus force | Effect and example |
|---|---|---|---|---|---|
| Topspin | Above centre of mass | Above the ball | Below the ball | Downwards | Ball dips, shorter flight. A tennis forehand can be hit hard and still land in, then kicks forward off the bounce. |
| Backspin | Below centre of mass | Below the ball | Above the ball | Upwards | Ball floats, longer flight. A golf drive carries further; a tennis or squash slice stays low and checks on the bounce. |
| Hook | Right of centre of mass | Right side | Left side | To the left | Right-handed golfer's shot curves right to left. Same spin as a right-footer curling a free kick with the inside of the foot. |
| Slice | Left of centre of mass | Left side | Right side | To the right | Right-handed golfer's shot curves left to right. Same spin as an outside-of-the-foot pass from a right-footer. |
Watch the word "slice". In golf it means sidespin. In tennis and squash a slice shot is hit with backspin.
Each diagram has exactly one mistake. Which part is wrong? There are seven diagrams in a random order, and the same part can be wrong more than once.
Define the Bernoulli principle and the Magnus force.
A right-handed golfer hits a drive that curves from right to left. Identify the type of spin and state where the eccentric force was applied to the ball.
Draw and label a diagram to show how backspin affects the flight of a golf ball.
Using the Bernoulli principle, explain how a tennis player uses topspin to hit a fast shot that still lands in the court.
A right-footed player curls a free kick around the wall with the inside of their foot, and the ball swerves from right to left. Explain how the spin causes the swerve.
Compare the flight of a tennis ball hit with topspin and one hit with backspin, at the same speed and angle of release.
The bounces in the simulator are illustrative only.