Skills & science · Today

How a ball curves

Real football fact

The facts

A spinning ball curves. As it spins it pushes the air to one side, so the air pushes the ball the other way. Scientists call this the Magnus effect.
Where you strike the ball sets the spin. Strike it right of centre and it curves left; strike it left of centre and it curves right.
Strike it hard through the middle, with almost no spin, and you get a knuckleball: it can wobble and dip in the air, so it is hard for a keeper to read.
In 1997 Roberto Carlos of Brazil bent a famous free kick against France with the outside of his left foot.

Why: The spinning ball drags a thin layer of air round with it. On one side that air meets the oncoming air head on, on the other side it moves with it. The air leaves the ball bent to one side, and the ball is pushed the other way.
Which way: The ball curves the way its front is turning. Spinning anticlockwise (seen from above), the front turns left, so it curves left.
Late bend: Scientists found that a spinning ball bends more and more as it slows down, so the curl can come late in the flight.
Under: Strike low on the ball and it spins backwards: the same push lifts it, so it floats. Strike over the top and it dips.
Knuckle: With almost no spin, the ball can move, dip and wobble in the air in ways nobody can predict. Juninho Pernambucano made this shot famous at Lyon in the 2000s.

To bend it, strike the ball off-centre and follow through across it. To hit it straight, strike right through the middle.