18 February 2013

Congrats to Australia!

Australia dominated West Indies to win the Women's Cricket World Cup.  The win marks the sixth overall for the Southern Stars.  Congratulations to Australia!

There is a great deal of fascinating physics in the sport of cricket.  A lot of research has focused on cricket ball aerodynamics.  My introduction to that line of research came in the form of well-written papers by Rabindra D Mehta of the NASA Ames Research Center in Moffett Field, California.  Mehta's classic 1985 paper "Aerodynamics of Sports Balls" in Annual Review of Fluid Mechanics (vol 17, pp 151-189) describes swing bowling.  His 2005 paper "An overview of cricket ball swing" in Sports Engineering (vol 8, pp 181-192) has cogent descriptions of reverse swing, a phenomenon achieved by fast (over 90 mph = 145 km/hr) bowlers or with balls that have been strategically scuffed.  Look up those papers if you want more details than what follows.

The side-to-side movement of a cricket ball boils down to getting an asymmetric deflection of air off the back side of the ball.  The rough seams usually help delay the separation of the boundary layer of air from the ball.  If you've ever thrown a Whiffle Ball, you know that the ball deflects toward the holes, ie the rougher part of the ball's surface.  Air moving over a cricket ball that has a seam predominately on one side and a smooth side on the other will make the ball move toward the seam side.  The reverse of that effect can happen if the ball is thrown very fast, fast enough that air flow over the entire ball is turbulent.  In that situation, the seams actually serve to help separate the boundary layer closer to the front of the ball compared to the smooth side.  That leads to reverse swing.

Cricket news doesn't make for much water-cooler chat in the US.  In countries like India, Australia, and England (just to name a few), sports fans care a great deal about cricket.  Though I played cricket only a few times while in graduate school, I enjoy following the World Cup for each gender.  I especially love all the great physics to be learned in studying cricket!

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