The Physics of a Corked Bat
The natural frequency of wooden bats is around 250 cycles per
second, or 250 Hertz. Because the ball leaves the bat so soon (1
millisecond), the energy transfer to the ball is not too
efficient. If the bat has been hollowed and corked, it's no
longer as stiff and it will get an even lower natural frequency
and an even less efficient transfer of energy to the bat. The
baseball bounces off the bat faster than the cork can store the
energy that could be put back in the ball. The cork might deaden
the sound of a hollowed out bat, but it doesn't propel the ball.
It can't. So, balls hit with corked bats don't go as far.
Aerodynamics & Curve Balls
For over a century baseball fans have debated the question of
whether a "curve ball does in fact curve". Only rarely has there
been objective scientific testing in order to verify what is so
obviously the appearance of a curve.
Igor Sikorsky's interest had stemmed from a phone call he
received from United Aircraft's Lauren (Deac) Lyman who over
lunch with Walter Neff of United Airlines, had discussed the
question of the trajectory of a baseball.
Mr. Sikorsky, who has a wind tunnel, called his engineers
together presenting the problem as follows: "Here we have a solid
sphere, moving rapidly in space and rotating on a vertical axis.
You see? ... the object is to elude the man with the stick". It
should be noted that baseball was a rather foreign endeavor to
Mr. Sikorsky.
Being a man of science he realized that a pitched ball, traveling
in a curved path, is an example of aerodynamic action in everyday
life. This force which causes a spinning ball to curve in flight
is the "Magnus effect".
Sikorsky's first problem was to determine how much spin a pitcher
could put on a baseball in the regulation sixty-foot, six-inch
distance from the mound to the plate. Engineers who were baseball
fans were glad to contribute some of their off-duty time. Careful
studies were made of fast-motion photographs showing the process
of a single pitch. Studying the change in the position of the
baseball's stitches from picture to picture proved that the rate
of rotation was about five revolutions for the pitch, or about
600 revolutions per minute.
The next problem was to determine if this spin could cause a
baseball to curve in flight. Testing began in the Sikorsky
Vertical Wind Tunnel during the next "stand-by time" between
aircraft model performance tests.
Since Big Leaguer's fast balls were officially clocked at 98.6
miles per hour, the forward speeds of the air moving through the
wind tunnel was varied between 80 and 110 miles per hour.
Using official National and American League baseballs - identical
except for their markings - Sikorsky impaled them on a slender
spike connected to the shaft of a small motor and rotated them
between zero and 1,200 revolutions per minute. The motor was
mounted on a delicately-balanced scale which measured the
direction and force of all pressure brought on the baseballs.
To observe maximum and minimum effects the baseballs were spiked
and rotated at two different angles. In one position four seams
met the wind during each revolution. This they found produced the
greatest amount of side force. Only two seams met the wind in the
other test position causing less friction and less side force.
Sikorsky's conclusions were that the baseball will in fact curve
in the sense that the spinning baseball does follows a steady
arc, rather than traveling in a straight line and then
"Breaking". A pitcher who can release the baseball so that four
seams meet the wind can "Break" as much as 19 inches. With the
same speed and rotation a two seam pitch will break 7.5 inches.
To the batter, who views the baseballs flight at an angle, it
appears that the baseball travels fairly straight most of the way
and then "Breaks" suddenly and sharply near the plate, this is an
optical illusion.
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