The Magnus Effect (aka how to bend it like beckham)
As someone who has suffered from Extreme Lack of Coordination for their entire life, I’m always amazed at professional athletes — especially those that demonstrate the things that I am least likely to ever achieve — aka, anything that involves hand-eye or foot-eye coordination. Since I can barely kick a ball into a net from straight on, I was fascinated by the video below that explains how great footballers can get the ball into the goal from well, anywhere on the pitch that is not straight on. There are also some really interesting animations and studies of soccer balls in this post, if you’re interested in further reading.
As it turns out, this is due to something called the Magnus Effect, which is when we observe a spinning ball moving in a curve away from its principal flight path. The direction of the ball is determined by the spin on the ball itself (back spin, top spin, side spin, etc). Perhaps some of the great footballers out there are also great physicists, but more likely, they just innately understand how to kick the ball so it spins the right way without thinking too much of the technicalities and equations that most of us normally associate with physics principles. But really, it is much more fun to play around with a soccer ball, so we’ll do that instead.
Understanding Spin: Practical Physics Lessons and the Magnus Effect
Since the trajectory of the ball is determined by the type of spin you put on it, what you really need to understand is where on the ball to kick with which part of you foot in order to impart the desired spin. But if you wanted to understand the Magnus Effect a bit more, check out the video below (which we’ve done a short summary for below).
- You generate spin on the ball based on where you kick it (the location on the ball that your foot touches) and the direction of force you apply
- The ball traveling through the air meets air flow resistance from the other direction
- Right around the ball, there is air drag circling around it (the ‘spin’)
- As oncoming air passes the ball, the side moving in the same direction as the spinning air drag will accelerate, following the curve of the ball
- The air on the other side that is moving against the spinning ball meets opposing air and can’t continue around the ball, so it goes straight
- This creates a net force of air to one side, forcing the ball to curve to the other side (see: Newton’s Third Law!)