How Do Soccer Balls Swerve?

During the 2014 World Cup, people around the world watched as 32 countries competed to be the best in the world at soccer (or football as most of the world calls it). With each World Cup, the host country typically designs a ball that ties in part of the country or region’s heritage. In 2014, it was no different as the Brazuca ball was used. MIT scientists, caught in World Cup fever, decided to investigate how a soccer ball swerves. Using the “Jabulani” ball from the 2010 World Cup in South Africa, and the “Brazuca” from the 2014 World Cup in Brazil, research was conducted to investigate how soccer players are able to curve the ball into the top corner of the net, away from many diving goalkeepers.

According to the article, variations in the different soccer balls can determine how predictable the ball will be in flight. It is also mentioned that the Brazuca ball has seams that are more than 50% longer than the Jabulani, a feature that John Bush, a professor of Applied Math at MIT, says makes the ball bend the wrong way. That’s right, its possible that two similar balls kicked the same way can curve in opposite directions varying on the surface of the ball. This .gif gives a visual example of the phenomenon occurring.

What makes this interesting is how the phenomenon could take different forms around the world. Soccer is a global sport played by people who are very wealthy and people in poverty. Most are able to play the game in North America on well-manicured turf or natural grass fields with authentic soccer balls. On the contrary, in less fortunate parts of the world, one can often find children using balls that are taped together on fields that might have a sand or clay surface that differs significantly from wealthier areas.

For a such a familiar phenomenon to many soccer players around the world, the explanation for it can seem pretty complex. Known as the Magnus Effect, the article claims that renowned scientist Isaac Newton was the first to describe it. He first noticed in tennis that topspin to the ball causes it to dip, while backspin will flatten out the trajectory. This application is brought to soccer, most commonly with free kicks, corners, and crossing passes. According to the article, a right-footed player will have a “right-to-left” hook, while a left-footed player will have the opposite.

The wrinkle to the Magnus Effect is how the direction of the curve can reverse. In the article, Professor Bush discusses how a completely smooth ball may change the curve direction. He explains this as a result of the ball surface creating a boundary layer. This essentially means the ball will curve in the expected direction. So why isn’t the reverse Magnus Effect a bigger deal? Its because soccer balls have never been completely smooth until only the last few years. It will be interesting to see if technology continues to emerge, and soccer balls evolve to eventually curve in the expected direction. If new, smooth soccer balls are manufactured and sold, would it change the way soccer is played in some parts of the world?  Would poorer places around the world still have to play with older soccer balls and therefore an older version of the game? Only time will tell as to what emerges for the game of soccer and its principal object.

## 2 thoughts on “How Do Soccer Balls Swerve?”

1. Michael Mandarino

I really liked this blog post. Over the past few years soccer has become one of my favorite sports to watch, and I love watching goals where the shooter seems to bend the ball around the wall. Philippe Coutinho is one of the best in the world at scoring these types of goals, and he did it in August in a win against Arsenal. Video: https://streamable.com/47rc

2. Jack Regar

This article was one of my favorites to read because I grew up playing soccer all of my life. The ball’s curve can change depending on the surface of the ball, and the way the subject is kicking the ball. If the subject kicks the ball with the outside of their dominant foot, assuming this player was right-footed, the ball is most likely to slice to towards the right. If the player curled it with the inside of their dominant foot, the ball is most likely going to hook towards the left.
Here is a video showing a slice with the outside of the player’s dominant right foot.
Here is a video showing a hook with the inside of the player’s dominant right foot.