U.
S. DEPARTMENT OF COMMERCE
SCIENCE AND TECHNOLOGY
Lewis L. Strauss,
Secretary
Washington 25, D. C.
FOR RELEASE
SUNDAY, MARCH 29, 1959
SF 59-10
(reproduced)
EMINENT SCIENTIST
REPORTS HOW FAR A BASEBALL CURVES
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Scientific
experiments show that the maximum curve a baseball pitcher can expect
to throw is about 17 inches.
The most effective
speed is about 100 feet per second, which is well within the capacity
of a professional pitcher.
Speed by itself,
however, has little effect. The important thing is the amount of
spin. The maximum curve of 17 inches is reached at 1,800 revolutions
per minute, which a professional can at least approach.
These conclusions
were announced today by Dr. Lyman J. Briggs, Director Emeritus of
the National Bureau of Standards, U.S. Department of Commerce, and
Director of Research for the National Geographic Society. Dr. Briggs,
who has been retired from NBS since 1945, conducted his experiments
partly because of their value in aerodynamics and partly because
he has been a baseball fan for most of his 84 years.
The serious
purpose of the study is to determine the relationship of spin to
deflection at different speeds. This problem has application to
ballistics at very low speeds.
Dr. Briggs'
research was conducted in laboratories at the National Bureau of
Standards when the equipment not needed for the bureau's work, and
at Griffith Stadium. There he had the cooperation of Cookie Lavagetto,
manager of the Washington Senators, and several pitchers, including
Pedro Ramos and Camilo Pascual. Ed Fitz Gerald was the catcher.
Two years ago
a visitor to the industrial building at NBS, listening to a serious
discussion of a mechanical problem by a young scientist, was startled
by a lound bang a few feet in back of him. It turned out to be Dr.
Briggs shooting baseballs at a paper target 60 feet away, using
a large mounted air gun.
In these experiments,
a baseball was rotated on a rubber tee, to give it spin, and was
struck by a wooden projectile shot from the gun. The projectile
drove the ball to the target. (In one wild shot, by the way, the
projectile broke a window.)
Dr. Briggs
tried photographing the ball in flight from above. This gave him
the speed and the curve, but it was impossible to mark the ball
so as to measure the spin. Since spin was so important, he moved
his experiments to the NBS wind tunnel, where speed and spin could
be directly measured.
The wind tunnel
experiments (described in Dr. Briggs' statement below) showed that
an increase in the speed of the pitch beyond 100 feet per second
reduced the curve only slightly and that the important thing was
the spin.
The results
of the research will be presented by Dr. Briggs in an article for
a scientific publication.
Born on a farm
north of Battle Creek, Mich., on May 7, 1874, Lyman J. Briggs never
attended high school, but entered Michigan State College by examination
at the age of 15. Four years later he was graduated second in his
class. He played in the outfield on a Michigan State baseball team.
The National
Bureau of Standards (of which he was Director 1933-1945) conducted
various experiments with golf balls at the request of the U.S. Golf
Association and with baseballs at the request of the War Department
and joint committee of the American and National Baseball Leagues.
In 1945 Dr. Briggs published a technical paper, "Methods for
Measuring the Coefficient of Restitution and the Spin of the Ball."
Coefficient of restitution refers to resiliency or bounce. He became
intrigued by the effect of spin and speed on baseball curves, but
put off his own research until his retirement from Government.
Dr. Briggs
is an outstanding physicist. In 1939 President Roosevelt made him
chairman of the original Uranium Committee to study the possibility
of using atomic energy in warfare. He directed much of the early
research leading to production of the atomic bomb.
Dr. Briggs'
Statement
His statement
on the baseball curve experiments follows:
Everyone who
has played baseball or golf or tennis knows that when a ball is
thrown or struck so as to make it spin, it usually curves or moves
sidewise out of the vertical plane in which it started.
What makes the
ball curve? To answer this question, let us imagine that the spinning
ball with its rough seams creates around itself a kind of whirlpool
of air, that stays with the ball when it is thrown forward into
still air. But the picture is easier to follow if we imagine that
the ball is not moving forward, but that the wind is blowing past
it. The relative motions are the same. Then on one side of the ball,
the motions of the wind and the whirlpool are in the same direction
and the whirlpool is speeded up. On the opposite side of the ball,
the whirlpool is moving against the wind and is slowed down. Now
it is well known from experiments with water flowing through a pipe
that has a constriction in it that the pressure in the constriction
is actually less than in front of or behind it; the velocity
is of course higher. Hence on the side of the spinning ball where
the velocity of the whirlpool has been increased, the air pressure
has been reduced; and on the opposite side, it has been increased.
This difference in pressure tends to push the ball sidewise or to
make it curve. It moves toward the side of the ball where the wind
and whirlpool are traveling together.
This explanation
was first given 100 years ago by a German engineer named Magnus,
to account for the curved path of a cannon ball. It is known as
the Magnus effect.
To what extent
does the curve of a baseball depend on its spin and speed? In such
measurements, it would of course be more realistic if the ball were
actually thrown by a pitcher, and we could photograph its flight
path with a stroboscopic camera flashing say 20 times a second.
But such measurements are hard to make. I tried something like this
with a ball propelled from an airgun, the camera being suspended
30 feet directly above a part of the flight path. This gave the
speed and curvature when the various positions of the ball were
projected in the photograph on a measuring scale on the floor below.
But the images were so small that the marks put on the ball to measure
the spin could not be seen. Since the spin is so important in making
a baseball curve, this line of attack was given up in favor wind
tunnel experiments, where the speed and spin could be directly measured.
In the wind
tunnel experiments, the baseball, spinning at a known speed (revolutions
per minute) about a vertical axis, was dropped to fall freely across
the onrushing horizontal wind-stream, the speed of which (in feet
per second) was known. The ball curved laterally across the tunnel
during this fall, and its point of impact was record by a light
smear of lamp black on the bottom of the ball striking a sheet of
cardboard fastened to the floor of the tunnel. The time of fall
across the wind-stream was 0.6 second.
As a result
of many measurements it was found for spins up to 1,800 rpm and
wind speeds up to 150 ft/sec that the lateral deflection (curve)
of the ball was directly proportional to the spin and to the square
of the wind speed, within small experimental errors.
We have now
to transpose these wind tunnel measurements to conditions encountered
in play. We are here concerned with the time required for
the gall to move approximately 60 feet from the pitcher's rubber
to the home plate. If the pitch had an average speed of 100 ft/sec,
then it would take 0.6 sec for the ball to traverse this distance.
But this is exactly the time required for the ball to fall across
the wind-stream in the tunnel measurements. So the measured lateral
deflections in the tunnel, 11.7 inches at 1,200 rpm and 17.5 inches
at 1,800 rpm, represent the maximum curvature predicted for
a pitched ball traveling 100 ft/sec.
For higher speeds,
the wind tunnel measurements have to be reduced, because the ball
is in the 60-foot zone between rubber and plate for a shorter time,
and the cross-wind forces accompanying the pitch have less time
to act.
The reduced
measurements are given in the following table.
Predicted
Maximum Curve of a Pitched Ball
Speed
ft/sec
|
Spin
rpm
|
Max.
Curve,
in 60 feet,
inches
|
75
|
1200 |
10.8 |
75 |
1800 |
16.7 |
100 |
1200 |
11.7 |
100 |
1800 |
17.5 |
125 |
1200 |
11.4 |
125 |
1800
|
16.5 |
150
|
1200 |
11.6 |
It will be seen that the speed of the pitched ball has little effect
on the amount it curves. The important thing is the amount of spin.
The values are
given for a ball spinning about a vertical axis. This is the most
favorable position in order to obtain the maximum curve. Usually
the spin axis of a pitched ball is inclined from the vertical, which
reduce the curvature. If the spin were horizontal, there would be
no sidewise deflection. Assuming the ball to be spinning clockwise,
as seen from the right, the resulting pitch would be a drop.
These wind tunnel
measurements bracketed the conditions encountered in play. According
to J. G. Taylor Spink, editor of the Sporting News, the fastest
pitch of record, 98.6 miles per hour (144 ft/sec) was thrown by
Bob Feller of the Cleveland Indians in 1947. This was the speed
across the plate, measured with an electronic device. The next fastest
pitch, 94.7 mph (138 ft/sec), was made by Atley Donald of the New
York Yankees in 1939.
It is of interest
to compare these fast pitches with the speed reached by a baseball
when dropped from a great height. This terminal velocity, about
140 per second, was measured in a vertical wind tunnel the National
Advisory Committee for Aeronautics by adjusting the wind speed until
the ball just floated in the upwardly-directed stream. The air resistance
was then equal to the weight of the ball.
Years ago, Charles
(Gabby) Street of the Washington Senators caught a ball dropped
from a window of the Washington Monument. The computed terminal
velocity for free fall in a vacuum from this height was 179
ft/sec; but owing to air resistance, it could not have exceeded
the 140 ft/sec measurement reported by Dr. H. L. Dryden from the
NACA.
The spin of
a pitched ball was measured with the cooperation of the pitching
staff of the Washington Ball Club. One end of a light flat tape
was fastened securely to the ball. The rest of the long tape, free
from twist, was laid loosely on the ground between the rubber and
the plate. After the ball had been caught, the number of complete
turns in the twisted tape was counted, which ranged from 15 or 16
down to 7 or 8 turns, while the ball traveled 60 feet. Assuming
that the speed of the pitch was 100 ft/sec, the maximum spin was1,600
rpm.
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Date created:
3/23/01
Last updated: 3/23/01
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