Magnus effect

The Magnus effect is the name given to the physical phenomenon whereby an object's rotation affects its path through a fluid, in particular, air. It is a product of various phenomena including the Bernoulli effect and the formation of boundary layers in the medium around moving objects.

Related Topics:
Rotation - Fluid - Air - Bernoulli effect - Boundary layer

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A spinning object creates a kind of whirlpool of rotating air about itself. On one side of the object, the motion of the whirlpool will be in the same direction as the windstream that the object is exposed to. On this side the velocity will be increased. On the other side, the motion of the whirlpool is in the opposite direction of the windstream and the velocity will be decreased. The pressure in the air is reduced from atmospheric pressure by an amount proportional to the square of the velocity, so the pressure will be lower on one side than the other causing an unbalanced force at right angles to the wind.

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This is not the only thing causing the deflection of the object. In addition to the Magnus force, the boundary layer of the flow is delayed on the side that is moving in the same direction as the free stream flow, and is advanced on the side moving against the flow. The flow is deflected away from the side moving against the flow, and this momentum change in the flow is balanced by a momentum change in the bullet in the opposite direction. Anything that disrupts the boundary layer will therefore tend to straighten out the trajectory. This is the reason for dimples on a golf ball: They disrupt the flow around the ball and tend to lessen the effects of spin.

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It is often referred to in the context of explaining otherwise mysterious but commonly observed movements of spinning balls in sport, especially golf, baseball, football and cricket. Another sport in which the effect is starkly observed is Table Tennis. An experienced player can place a wide array of spins on the ball, the effects of which are an integral part of the sport itself. Table Tennis rackets often have outer layers made of rubber to give the racket maximum grip against the ball to facilitate spinning.

Related Topics:
Sport - Golf - Baseball - Football - Cricket - Table Tennis

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It is worth noting, however, that the Magnus effect is not responsible for the movement of a cricket ball seen in swing bowling.

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German physicist Heinrich Magnus first described the effect in 1853.

Related Topics:
German - Physicist - Heinrich Magnus - 1853

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