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The Physics of Soccer

We're into the semifinals of the World Cup and if you've been watching, you've been graced with nail biting finishes and spectacular, curling goals. If you haven't been watching you no doubt know the phrase to "Bend it like Beckham", probably because you've seen or heard of the 2002 film of the same name.

If this is all totally new to you, here's what it means to curl/curve/bend a ball "like Beckham".

Note: not David Beckham.

The way it works is pretty simple, even intuitive. It's known as the Magnus Effect. As an object spins, the air on one side of the ball travels with its rotation. On the opposite side the air is moving against its rotation, putting additional force on that side of the ball, causing it to curve. Check out the video below rom Veritasium for a full explanation.

There's more at play here than just the spin, however. The smoothness of the ball has a major impact on how it will travel. More dimpled or rougher balls will travel on a more predictable path. Conversely, smooth soccer balls can actually travel the "wrong direction," which means that a smooth ball kicked the same way by the same player can actually curve opposite way of a rougher ball, essentially negating the Magnus Effect.

The ideal soccer ball is a perfect sphere with a skin that has the right amount of ridges and dimples to help it fly more stably. That's why since 1970 Adidas has continuously been tweaking the design of the World Cup ball, ranging from the 32 smooth, octagonal sections featured on the 1970 World Cup ball to the 6 oddly shaped, pimple covered panels today. In between, lighter versions have soared over goalies heads and smoother iterations have traveled in strange ways. Always, the fans have something to complain about, besides the refs.

Of course, in four years Adidas will have showed up to the pitch with a redesigned ball and it will be that much closer to perfection. For now it's probably best to just watch the World Cup and enjoy the frenzy that surrounds. But at least next time you see a curling shot go over a line of defenders you'll know all about the physics at play.

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