# Why does a cricket ball swing or a baseball curve?

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Why does a cricket ball swing or a baseball curve?
FLUID FLOW MOTION OF OBJECTS IN FLUIDS How can a plane fly? Why does a cricket ball swing or a baseball curve? Why does a golf ball have dimples? web notes: lect6a.ppt flow4.pdf flight.pdf

Resultant FR Lift FL drag FD Motion of object through fluid
FORCES ACTING ON OBJECT MOVING THROUGH FLUID Lift FL drag FD Resultant FR Motion of object through fluid Fluid moving around stationary object

The pattern is symmetrical
Uniform motion of an object through an ideal fluid ( = 0) The pattern is symmetrical  FR = 0 C A B D

Drag force frictional drag (viscosity) pressure drag (eddies – lower pressure)

NO CURVE Drag force due to pressure difference low pressure region
motion of air Drag force due to pressure difference motion of object low pressure region rotational KE of eddies  heating effect  increase in internal energy  temperature increases NO CURVE Drag force is opposite to the direction of motion high pressure region

ball: curved flight flow speed (high) vair + v  reduced pressure v
motion of air Drag force due to pressure difference ball: curved flight motion of object flow speed (high) vair + v  reduced pressure v vair (vball) MAGNUS EFFECT flow speed (low) vair - v  increased pressure v Boundary layer – air sticks to ball (viscosity) – air dragged around with ball high pressure region low pressure region

Professional golf drive
Initial speed v0 ~ 70 m.s-1 Angle ~ 6° Spin  ~ 3500 rpm Range ~ 100 m (no Magnus effect) Range ~ 300 m (Magnus effect)

How can a plane fly?

FLift = CL ½  vs2 A

NO !!! rest in peace

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