Measuring Ball Speed

MATERIALS NEEDED:

Data from previous experiment, measuring the time of flight of the tennis ball. If this is not available, some sample data is provided here:

Sample data from a match at the Sybase Open, 1997: Pete Sampras serving to Alex Radelescu 0.367 seconds from serve to bounce, 0.233 seconds from bounce to Radelescu's racket. The serve was at the baseline, the bounce was very close to the far service line, and the return hit was at the far baseline. Radar gun recorded a speed of 124 mph.

STEPS TO FOLLOW:

one Look up the dimensions of a tennis court, and estimate the distance traveled by the ball from the server to the receiver. It is probably close to the full length of the court. Using what you measured as the full time between serve and return, calculate the average speed of the ball. (What are the units of the speed that you just calculated?)

two To convert these units into miles per hour (to compare to the radar gun measurements), you need some additional information. A mile is 5280 feet, and there are 3600 seconds in an hour. A convenient way to do this conversion is as follows:

(click here for equation)
Notice how each of the quantities in parentheses is equivalent to 1, since what is in the numerator is equal to what is in the denominator. If you multiply all of the units together the feet and seconds will cancel, leaving units of miles per hour. All that is left is for you to multiply the numbers together to get the speed in the right units.

three Compare this to the radar gun measurement, if one is available.

four Why do you think the average speed that you calculated and the speed recorded by the radar gun are different?

five Now estimate the distance traveled from the serve to the bounce, in feet, and calculate the average speed of the ball for this first flight. Convert the speed you just calculated into miles per hour.

six Estimate the distance from the bounce to the return hit, and calculate the average speed for this second flight. Convert this speed to miles per hour.

seven How do the average speeds before and after the bounce compare?

Comments? drop tennisnet@cislunar.com a line.
Last modified: Sat Nov 15 16:14:06 PST 1997