Top spin

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For the Top Spin video game, see Top Spin Tennis.

For the amusement park ride developed by HUSS Maschinenfabrik, see Top Spin (ride).

In racquet sports a ball gets top spin when the racquet hits it while moving upwards. Top spin makes the ball come down earlier so it can be hit harder and faster. Tennis players use top spin to keep their fast strokes in the court. In most court surfaces, top spin also makes the ball bounce higher.

Billiards players use top spin to keep the cue ball moving also after it hits the other balls. They get top spin literally by hitting the top of the ball. The same goes for golf players, although for them top spin is undesirable as they generally want the ball to fly further than closer.

Bernoulli's principle explains why this happens. Imagine a stationary ball in a wind tunnel, air moving from right to left. Or if you prefer, think of a tennis court in a calm day watching the ball go from left to right. In both cases, a ball with top spin rotates clockwise as you see it.

Now think of the airflow from the ball's perspective (this is easier if you think it is in a wind tunnel). The top of the ball is moving right, or forwards against the airflow which slows down the airflow on the top surface. Just the opposite occurs for the bottom of the ball. It moves to the same direction as the airflow, and accelerates the airflow on the bottom. With some abuse of physics, you can compare the movement of the top of the ball with skid braking on tarmac (slower airflow) and the movement of bottom as burning rubber during a quick acceleration (faster airflow).

Bernoulli found out that an accelerating airflow reduces pressure and a decelerating airflow increases it. The top of the ball faces a slower airflow with higher pressure and bottom of the ball has a faster airflow with lower pressure, so the higher pressure on top pushes the ball down towards the lower pressure. This explains why the ball comes down faster than a ball without top spin.