Tennis Physics: Part One

When I'm not watching tennis, I participate in space missions for a living.  I just got the Tennis Channel in my house, and I couldn't help but notice a few things—now that I'm watching more regularly—about the physics of tennis.

I thought I'd write some briefs notes on the subject as I get the inspiration.

"Feeding off the pace" 

I've heard that phrase a million times during the commentary.  It was a long time before I understood what "pace" was (why don't they just call it "velocity?").  A player like Giles Simon, who is as skinny as Rafa Nadal is muscular, can generate as strong of a forehand.  Or does he?  

When you bounce a ball off of a wall, the ball will come back without losing much momentum.  But if the wall moves toward you at the same time, then momentum is added to the ball.  If the wall is a tennis racket, so much the better.  If the ball is stuck between two walls moving toward each other, then it picks up energy quickly.

If you are a player "feeding off of the pace" then you are taking advantage of the manner in which momentum is preserved for a ball stuck between two moving walls (tennis rackets). 

'Reaction Wheels'  

While watching Brad Gilbert clowning around in this video on ESPN, I noted that Brad mentioned that players twist with their upper body to generate the modern power forehand.  They twist around their waist with their hips and shoulders.

Well, this is just what a spacecraft does, way off in space.  Not to generate a power forehand, but just to turn itself. To keep a spacecraft stable, a device called "reaction wheels" were introduced.  If you want to turn the spacecraft one way, you have to turn the reaction wheels the other way.

What is impressive is for players to generate a power forehand by twisting at the middle implies a tremendous core strength.  They are not just pushing against the ground. Like a machine in space, they have to maintain stability and generate that turn by twisting two sides of their body.

That's it for now.  Please let me know if these notes were completely boring or somewhat interesting!