Strategic Science: Exploring the Physics Behind Volleyball Serves and its Outcome

Author: Seoyeong Jang (Crystal Jang)

There are two major service tactics in volleyball - Float serve and back spin serve. Both services are known to be extremely powerful, but they have their own distinct differences. However, before getting started, it is important to note and understand the Magnus effect. The definition of Magnus effect is a force that is exerted on a rapidly spinning cylinder or sphere moving through air which makes the object bend away from the intended direction of travel, making it curl away. This is a key concept of both float and back spin serve.

For example, float serves, as you can infer from its name, will ‘float’ on air unexpectedly without spinning. It can be achieved by hitting near the centre of the ball without snapping the wrist. The ball will suddenly drop down, making it hard for players to react. Not only that, another powerful characteristic of a float serve is that the ball will move up and forwards with random movements in air. As the volleyball isn’t completely smooth and that there is no spin, the airflow around the ball becomes unstable. The uneven air pressure zones cause the forces on the balls to be unbalanced, reasoning for the sudden drops. 

Diagram of a float serve (Image source: wovc.org)

However, the back spin serve majorly focuses on the spinning motion of the volleyball. It is performed by hitting the bottom of the ball with a wrist snap. Do not confuse this serve with another popular service skill, top spin serve. It may not be as powerful as a top spin serve or a float serve, but the odd spin cycle makes it challenging to receive and dig, startling and disrupting the game flow effectively. 

Magnus effect is exerted on this ball upwards, prolonging the airtime of the ball. The air above the ball creates friction, dragging the ball backwards and causes it to spin, while the air below the ball stays still. The upwards lift force opposes the gravitational pull, therefore allowing the ball to stay in air for longer. The two forces acting in opposite directions decrease the resultant force. According to Newton’s second law, F=ma, acceleration decreases as force decreases, explaining this movement. This also confuses the opponent, as they cannot predict where the ball will land, or whether it will be in or out of the court. 

From left to right - back spin, top spin (Image source: wovc.org)

As a side note - I’m sure many of you just like me would’ve wondered why volleyball players bounce the ball on the floor before their serve. Surprisingly, there aren’t that many physical reasons that contribute to that action. Some being the athlete’s routine and mental preparation, or feeling the air inside the ball, but nothing to do with the quality of the service itself, as the air inside the ball only swirls temporarily before the athlete holds it up to hit.

Diagram of Magnus effect being exerted on a ball (Image source: project air)

Cover Photo: Pexels