Tennis Physics
GREAT TENNIS PLAYERS HAVE AN INUITIVE SENSE OF JUST WHERE ON A
RACKET TO HIT THE BALL.  YEARS OF EXPERIENCE IS BOUND TO TEACH A
PLAYER HOW TO GIVE A BALL THE MOST POWER, OR THE MOST SPIN.  BUT
INTUITION ON HOW THINGS WORK IS NEVER QUITE GOOD ENOUGH FOR
SCIENTISTS--THEY LIKE TO FIGURE OUT WHY.  ROD CROSS IS ONE SUCH
SCIENTIST.  HE'S A PHYSICIST AT THE UNIVERSITY OF SIDNEY IN AUSTRALIA,
AND HE SET OUT TO STUDY THE FABLED "SWEET SPOT" ON THE RACKET--THE
BEST PLACE POSSIBLE TO HIT THE BALL.  INSTEAD HE FOUND A DEAD SPOT.

Cross: "The ball doesn't bounce . . . at all at the tip of the racket. . . there is
a dead spot. . . that's normally where I hit the ball.  

HE FOUND THE SPOT BY CLAMPING DOWN A TENNIS RACKET AND
DROPPING BALLS ONTO IT.  WHEN DROPPED AT THE TIP, THE BALL WOULD
STOP DEAD. 

Cross: "What happens in the dead spot is a well known effect in physics
that anyone who has played pool will know--when one ball is at rest and
another ball comes in and hits it the incident ball suddenly stops and the
ball that was hit takes off.   That's what was happening with the tennis
racket . . . the tip of the racket has a mass that's about the same as the
mass of a tennis ball."

SO WHEN THE BALL HITS THE TIP OF THE RACKET, JUST LIKE A BILLIARD BALL, IT
STOPS DEAD, TRANSFERRING ALL OF ITS ENERGY OVER TO THE TENNIS
RACKET WHICH RECOILS.  THE ODD THING IS THAT THIS SPOT IS THE PERFECT
PLACE TO HIT A SERVE.  IN THE CASE OF A SERVE THE BALL IS ESSENTIALLY
HANGING STATIONARY IN THE AIR, AND THE TENNIS RACKET IS MOVING.

Cross: "What's going to happen is the racket is going to stop and the ball
will take off." 

OF COURSE IF YOU'VE WATCHED A SERVE, THE RACKET DOESN'T STOP
COMPLETELY, BUT CROSS DISCOVERED THAT ALL ROTATION IN THE RACKET
DOES STOP.  OF COURSE THE BIG QUESTION HERE, IS WHETHER THIS
INFORMATION GOING TO HELP ANY ONE'S GAME . . .

Cross: "I started concentrating really hard on serving form the tip. . but I
was concentrating so hard that I messed up the points all the time. . ."