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Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume IV (1876-1877)

McMurphy, J. G.
Rotation as a factor of motion,   pp. [235]-240 PDF (1.5 MB)


Page 239


Rotation as a Factor of Mfotion.
resistance finally throws the ball to the right If the ball had
balloted on the left side last, in leaving the muzzle, it would have
been deflected to the right by touch and afterwards to the left by
resistance and reaction of the compressed air. Thus it is possible
with a smooth-bored gan to " shoot round " a nearer object
in
direct line and hit a more remote object behind it.
  I wish to give but one more instance of the effect of rotation
on direct motion. It is vulgarly called " curved ball."
It may
be witnessed in any good base-ball match. The pitcher desires
to elude the strokes of the batter; after delivering a few balls in
simple parabolic curves or with axial rotations, he will deliver the
ball from the hand in-such a way that when the ball leaves the
hand the fingers touch it from below, causing the underside to be
retarded while the upperside moves forward. Then the ball ro-
tates upon a horizontal transverse axis, relative to its motion of
translation. The greatest resistance from compressed air is in
front and above the moving ball. The ball seeks a path of less
resistance, preserving its plane of rotation and drops enough to
form a depressed curve. By a skillful adjustment of rotation and
translation, the pitcher is able to produce about such a curve. as
he wishes. To the batter the ball seems coming toward a point
it is destined to fall short of. Again, by delivering the ball from
the hand with the fingers touching above. a backward rotation is
produced on the top of the ball and a forward motion to the under
side. Such a ball continues its course until accumulated resist-
ance of air from ahead and below throws it upward. So the
batter sees the ball coming toward a point it is destined to pass
clearly above. By skillful manipulation the right side of the de-
liverer the ball may be retarded, and the ball will curve to the
right, and by retarding the left side it will curve to the left. The
amount of curvature is variously estimated by different persons.  %
With the rotation or twist of the best pitcher, it is no uncommon
thing to make a ball curve a yard from its direct path, while many
cannot effect any curve.
  This purports to be only the outline of a subject worthy of
much greater investigation, in its relation to great scientific prob-
lems.
239


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