11th Notes 12th Assignments

Magnus effect and dynamic lift

Magnus effect and dynamic lift-

The upward force experience by a body when it moves through a fluid is called dynamic lift . Such a lift is felt by airfoil , aircraft win etc. Couse behind it can be explained by Bernoulli’s theorem . It also explain why a spinning ball is deviated from its parabolic path .This deviation is usually observed in many games like cricket, football golf, tennis etc.

As a ball moves through air without spinning , it divides the streamline  above and below it symmetrically . Thus there is no pressure difference on the two sides of the ball.

But when a ball spins as it moves through air , it drags along a layer of air with itself. When the ball moves forward , the air ahead of the ball rushes backward to fill the space left vacant by the ball. Thus the streamlines of air around this ball is shown in the fig. given below.

The velocity of air above the ball opposite to the direction of spin and it is in the direction below the ball. Thus the relative velocity of air  with respect to the ball is larger at the upper part than that is in the region below  the ball . The streamline thus gets crowded above and rarified below .This cause the pressure above the to be smaller and that below it to be greater . This pressure difference causes an upward force on the ball. Hence the ball experiences a dynamic lift and is deviated from its path . This effect arising due to spinning of the ball is called ‘Magnus effect’.

Airfoil and lift on aircraft wing:-  An airfoil is streamlined shaped , Solid body that is capable of generating a dynamic lift as it moves through a fluid .  streamline shape is special shape given to bodies moving in fluids, So as to produce minimum drag .

The cross-section of air wings is also shaped like that  .Its upper portion is more curved then the lower surface .Its front edge is broader and the rear edge is narrow . When the airfoil moves through air , streamlines of air moves backward . The air above the foil has to travel a longer distance then that  below in the same time . Thus the flow speed on top becomes greater then that below it . The higher speed on reduces air pressure there. This pressure difference causes to lift the foil. Such dynamic lift also acts on the wings of an air craft and balances the weight of the plane.