ROD CROSS HOME PAGE

A recent (2009) photo

evidence for murder (UNSW Press) NEW BOOK (Oct 09)

Late Night Live Interview ABC Radio National 7 Oct 2009

University of Sydney Media Office Interview 23 Oct 2009

Channel 10 Movie Clip (QuickTime) from “A Model Daughter” 4 Nov 2009

Technical Tennis by Rod Cross and Crawford Lindsey

Available from www.racquettech.com, amazon.com etc (only $11 for priceless information!)

Remember this: “Sex is good but tennis lasts longer” Freud, 1938.

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SPORTS PHYSICS

(At 1000 f/s) (At 1000 f/s)

Superball 1000 f/s (note spin reversal)

HOOP Bounce1, Bounce2, Bounce3 at 600 fps The hoop slides then grips before bouncing, in the same but in a much more obvious manner than a ball. It is also obvious, especially in bounce2, that the normal reaction force does not act through the centre of mass and therefore exerts a strong torque on the hoop, reducing the spin rate. The same effect occurs with spherical balls.

TENNIS BALL at 3000 f/s incident at 30 m/s on clay and on grass (copyright by ITF). Can be viewed with QuickTime or RealPlayer and is in H.264 compressed format. Note how clay sticks to the ball and is then spun off. The grass here was longer than normally seen at Wimbledon. Grass is a faster surface than clay, even when the grass is long. You can work out the bounce speed, spin and angle yourself from this film.

TENNIS STRINGS at 1000 frames/sec (using a 725 g boule incident at low speed)

COLLISIONS and BOUNCE OF AN OVAL FOOTBALL

BILLIARDS

MORE TENNIS and FIVE WAYS TO WIN A POINT and TENNIS STATISTICS

BALL TRAJECTORIES

WOBBLE BOARDS & MUSICAL SAWS

LISTEN TO A BELL (recorded at the same volume and ball speed) hit with

(a) a golf ball or (b) a tennis ball

Why are the sounds so different? It’s the same fundamental reason that some bats and racquets have bigger sweet spots than others. The amount of vibration depends on the ratio of impact duration to the vibration period. The bell might sound tinny if you use internal speakers. Try it anyway as a test of the bass response of your internal speakers. The fundamental frequency is 975 Hz. Internal speakers will not respond at all to the f < 200Hz racquet sounds included on the tennis page.

This is a pretty picture of a golf ball and an 8mm thick slice of a large superball sitting on a slab of polished granite. The ball spins faster when it bounces off the superball slice since the tangential coefficient of restitution is much larger. A golf ball that spins faster will travel further. Click on photo to see a simplified explanation of why the ball spins faster. The same effect occurs with tennis strings.

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FORENSIC PHYSICS

Some cases I have worked on with NSW Police and Coroner ______________________________________________________________

Brief CV

Born 1943. Lived in Berry, NSW until age 14 then moved to Forbes. B.Sc. Dip. Ed at Sydney University. PhD in plasma physics in 1968. From 1968 to 1996 I worked in the Plasma Physics Department at Sydney University, specialising in Alfven wave studies in the TORTUS tokamak. I retired in 2003 as an Honorary member of staff, to continue work on the physics of sport and forensic physics.

PUBLICATIONS (and TENNIS MAGAZINE ARTICLES)