Why does a football curve in the air?

KohakuOn a free kick, a ball sometimes curves in the air and goes into the goal. How does that happen?

The answer in 30 seconds

The key is the spin of the ball.

A spinning ball drags the air around it, so the pressure becomes different on each side. The difference pushes the ball sideways, and it curves. This is called the Magnus effect. Curving free kicks are explained by the same force.

A white and navy blue football lying on grass — A football curves in the air when it is kicked with spin.Photo: Wutthichai Charoenburi from Bangkok / CC BY 2.0 / Wikimedia Commons

Spin changes the flow of air

A football (soccer) ball curves in the air because it is spinning as it flies. When you kick the edge of the ball so that it spins, the air flowing around it is pulled in the direction of the spin.

Pushed sideways by a pressure difference

At that moment, air flows fast on one side of the ball and slowly on the other. The side where the air moves fast has lower pressure, and the other side has higher pressure. This difference pushes the ball sideways. The force acts at a right angle to both the axis of the spin and the flow of the air. This sideways drift is called the Magnus effect. NASA's Glenn Research Center also explains the force on a spinning ball as the source of the "bend," a curving kick that gets around the goalkeeper.

Figure: How a ball is pushed sideways

Roberto Carlos's free kick

A well-known example is the free kick taken by Brazil's Roberto Carlos in 1997. According to the magazine Physics World, the ball was placed about 30 m from the goal. Struck with the outside of his left foot, the ball curved sharply and went into the goal. Scientists have used it as a subject for studying how a ball curves.

KohakuRoberto Carlos's free kick even became a subject that scientists studied, they say.

The farther the kick, the more it spirals

In 2010, physicists in Paris, including David Quéré, published a study of this shot. They confirmed that the Magnus effect explains the curve, and they also found that as the ball slows down, its path bends like a spiral. With a football, this spiral is said to show up after the ball has travelled about 40 m.

Want to know more?

NASA gives a formula for the size of the force that bends a ball, using the ball's size, its spin, its speed and more.
The 2010 study was done by physicists at ESPCI and the Ecole Polytechnique in Paris, and the results were published in the journal New Journal of Physics.

KohakuA difference in the flow of air, created by the spin, was pushing the ball sideways.

Quick quiz: test yourself

Why does a ball curve in the air?

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Force made by its spin
A constant crosswind
The ball warps when kicked

Force made by its spin A spinning ball makes the air flow differently on each side, and the pressure difference pushes it sideways. This is called the Magnus effect.

Sources

The physics of footballPhysics World (Institute of Physics)
Soccer Ball Aerodynamics (Lift of a spinning ball)NASA Glenn Research Center
Scientists uncover secret of Roberto Carlos goalNBC News (Associated Press)

This article was written after checking the sources above as of 2026-10-03. Explanations may change as research progresses. Photo credits are shown below each photo.