1. 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

2. 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

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

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

5. 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

6. 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

8. 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)

10. How can a plane fly?

15. FLift = CL ½  vs2 A

16. NO !!! rest in peace