who knows about magnus effect,please guide me?

Answer 1

What are you looking for, specfically?

Have you tried searching this term? The first hit in Google is a Wikipedia page, which offers an explanation:

http://en.wikipedia.org/wiki/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.

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.

The overall behaviour is similar to that around an aerofoil (see lift force) with a circulation which is generated by the mechanical rotation, rather than by aerofoil action.

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 object 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 energise the boundary layer, making it turbulent which helps to reduce pressure drag due to early flow separation (see drag).

It is often referred to in the context of explaining otherwise mysterious but commonly observed movements of spinning balls in sport, especially tennis, volleyball, golf, baseball, association football (soccer) and cricket. The sport in which the effect is perhaps most starkly observed is table tennis, mostly due to the ball being very small and low in density. 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 bats usually have outer layers made of rubber to give the racket maximum grip against the ball to facilitate spinning.

Contrary to what some think, the Magnus effect is not responsible for the movement of a cricket ball seen in swing bowling.

German physicist Heinrich Magnus first described the effect in 1853 but according to James Gleick [1] Isaac Newton described it and correctly theorised about the cause 180 years earlier after observing tennis players in his Cambridge college.

Answer 2

Basically it's what causes windage in bullet travel, or is what causes a ball with top spin to dive or a ball with backspin to fly longer. Essentially, rotation of an axisymmetric body (cylinder, sphere) will cause the local velocity at the windward surface to be high, and lower at the leeward side. This causes a lift force that is in the direction of the most windward side.