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Magnus effect
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A spinning ball curves because of pressure differences.
A spinning ball in air drags the air along its surface, creating a pressure difference that curves its path. Used in football free kicks and topspin.
Backspin on a golf ball adds lift.
The spin deflects air to one side, so the ball is pushed to the opposite side.
In more detail
The Magnus effect is the sideways force on a spinning ball moving through air. The spin drags air around one side, making the flow faster there and the pressure lower, which curves the ball.
Real-world uses
- Football bananas and tennis topspin are shaped by the Magnus effect.
- Spinning cylinders are used in ship propulsion systems called Flettner rotors.
- Footballers and tennis players use the Magnus effect to make the ball curve in the air.
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Frequently asked questions
Why does a spinning ball curve?
The spin makes air move faster on one side, which lowers the pressure on that side and pushes the ball.
Does the effect need air?
Yes. In a vacuum, a spinning ball does not curve.
Why does a spinning ball curve?
The spin drags air round one side, speeding it up and lowering the pressure, so the ball is pushed toward that side.
Related topics in Fluids & Elasticity
Venturi meter · Pitot tube · Lift on a wing · Viscosity · Poiseuille's equation · Stokes' law