# In tennis, why does topspin serve bounce higher than flat serve?

When receiving servers (while playing tennis), I've noticed that the tennis ball seems to bounce up higher on me when the server uses a topspin serve than when the server hits a flat serve. Why is that?

Is it because of something about how the spin affects the bounce of the ball (i.e., the effect of the spin during the time when the tennis ball is in contact with the court)? Is it because of how the spin affects the flight of the ball while it is in the air? Perhaps it's because topspin serves tend to be hit with a higher, "loopier" trajectory, and this changes the angle of incidence when the ball hits the court during the bounce? Or maybe it's something else entirely? What would you expect the effect of the topspin to be on the trajectory of the ball, based upon physical principles?

Background on tennis: When serving, the server has to hit the tennis ball over the net and then into the service box; the ball is required to bounce within the service box. The receiver stands back a bit, and after it bounces up, the receiver hits it back.

A flat serve is a serve where the ball has no spin. A topspin serve is a serve with topspin: the top of the tennis ball is rotating forward (in the direction of the ball's travel) and the bottom of the ball is moving backward (opposite the direction of the ball's travel). Topspin causes the tennis ball to "curve downwards", due to the Magnus effect.

From the server's perspective, topspin is useful, because it means the server can hit the ball higher over the net and the serve will still go in. That allows a topspin serve to be more reliable: the server has more margin for error. In contrast, with a flat serve, the serve has to be aimed very precisely: aim too high, and the ball will "go long" and bounce outside of the service box; aim too low, and the ball will hit the net. A flat serve will usually look like a "line drive" (the path of the ball is close to a straight line), while a top spin serve will look more "loopy" (the ball goes higher over the net, then swerves down).

Flat serves usually travel faster. With a topspin serves, the ball usually doesn't have quite as much velocity (I imagine some of the energy of the server is spent on imparting spin, rather than propelling the ball forward). Nonetheless, from my personal experience, it feels like when I am receiving a topspin serve, the ball bounces up higher and often gets out of my comfort zone: the flat serve might bounce up to waist level, where it's comfortable to hit the ball, but the topspin serve might bounce up to shoulder level, where it's less comfortable. Why does this happen? Or, is it an illusion?

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More Phys.SE posts on Magnus effect: physics.stackexchange.com/search?q=magnus+effect – Qmechanic May 15 '13 at 6:45