Topspin forearm in sports

The topspin forehand is one of the must have shots on the tennis court. This effect is used in many sport like baseball, cricket, racket sports, football and cue sports.

We can’t see topspin effect in the curved trajectory off balls which are thrown, kicked or hit and which are given a spin. In fact, the ball seems to have a straight-line trajectory but suddenly it deviates from its first trajectory.

This effect is due to its interactions with the air, these interactions create forces which can’t drop the ball.

Let’s see a small video to clarify this

How backspin affect a basketball when dropped from 140m up

The topspin effect is due to the Magnus effect. It was discovered by Heinrich Gustav Magnus (1802-1870), a German physicist. It is important in many ball sports. Moreover, it affects spinning missiles, and has some engineering uses.

Physical Explanation

The first thing is to kick the ball and the most important is to apply a rotation to the ball. We place this ball on a fluid, for example the air. Initially, just after have been kicked the ball has stored lots of energy and move with a high speed. During this state the ball isn’t subject to the opposition of the fluid. The ball move linearly.

When the ball slows, the fluid slide all around the ball. Thus, the ball is strongly subject to the fluid interactions and the ball slow down.

In this condition the Magnus effect take place. The ball is always in rotation. It speeds up the flow on one hand and slow down the flow on the other hand. The more the fluid speeds up more the more the pressure increase. This creates an excessive pressure on one hand and a depression on the other hand.

The ball is rationally attracted by the depression. Thus, it diverts to its initial trajectory

Moreover, some flying machines and ship have been built using the Magnus effect. Most of the time these machines include rotating cylinder to allow the propulsion of it.

Recently The iCar 101 Project a crowdfunded project run by the Aeromobile European Association was born. They use Magnus effect with spinning wings.

For more information: http://www.icar-101.com/icar/index.php