Ball/Court Interaction (Page 16)

She believed that the grass court ball would reach a player standing at the same position, first. We arbitrarily selected 7 feet from the bounce.

The results are clear - the grass court ball not only reached the player first, but it had a faster velocity when it reached the player. This was because its horizontal velocity V_x was faster than the balls from the other courts.

There are some very interesting things to note in these charts - and they are fun to play around with. When you open the charts up you will see columns for time, V_x, V_y , V and the distance from the bounce in inches.

Seven feet is 84 inches. Go down the distance column for the grass court until you reach 84 inches. (Actually, there is one entry at 83.1 inches and the next entry at 85.3 inches.) Look at the time and velocities: the time is roughly .3 seconds, the horizontal velocity is 15.66 miles/hour, the total velocity is about 15.70 miles/hour.

Look at the data for the green court. The ball doesn't reach 84 inches until the time is .337, the horizontal velocity is 13.6 and the total velocity is 14.08. That's almost 2 miles/hour less.

So the grass ball reaches a player sooner. You have less time to react, and that's what qualifies a grass court as "faster".

If you look farther down the grass court court at 98.4 inches from the bounce, you will notice something else - the vertical velocity becomes negative - this means the ball is now dropping. If you look at the green clay court the ball is still climbing. The grass ball starts dropping to the ground sooner than the balls off of the other court - a player has less time to react for this reason as well.