LETTERS TO THE EDITORS
Mastering Spin
To the Editors:
In "Predicting a Baseball's Path" (May-June), A. Terry
Bahill, David G. Baldwin and Jayendran Venkateswaran state that a
95-mile-per-hour pitch drops 1.7 feet between the release point and
the contact point and that a 75-mile-per-hour pitch drops 5.7 feet;
both drops are due to gravity. These numbers are incorrect.
The relevant relationships are quite simple: Time of flight equals
distance (60 feet) divided by velocity, and vertical drop equals
one-half the gravitational constant times the square of the time of
flight. Using a gravitational constant of 32 feet per second
squared, the vertical drop for the 95 mile-per-hour pitch is 2.97
feet and the vertical drop for the 75 mile-per-hour pitch is 4.76 feet.
George C. Messenger
Las Vegas, Nevada
The authors respond:
The following explanation should help to clear up the
misunderstanding. Our article said that as soon as a pitcher
releases a ball, it's in gravitational free fall, whether it's a
blistering fastball or a gentle change-up. A 95-mile-per-hour
fastball drops 1.7 feet between the pitcher's release point and the
point of a bat-ball collision. Slower pitches fall more. A
75-mile-per-hour curveball, for instance, drops 5.7 feet. Clearly, a
ball's pathway to the plate also depends on other forces.
The numbers in the article gave the drop due to both gravity and
spin. The distance between the front of the rubber and the back tip
of the plate is 60.5 feet. The pitcher releases the ball about 5
feet in front of the rubber, and the batter hits the ball about 1.5
feet in front of the plate. So the ball is in the air about 52.5
feet. For this distance, the drops due to gravity and spin are given
in the table below.