Secret of Pitch—Be a Real Pitcher
By TSOY, Man-Ching
Baseball is one of the
most popular sports in
the world that nevertheless has an element of science in it. Having a good
pitcher in a team is essential in winning baseball
games as the variation between pitches thrown by
the pitcher enhances the
defensive strategy of the
team. It is extremely difficult for batters to hit the
ball if the pitcher can
master the different types
of pitches, even the slightest difference among trajectory, movement and
speed can mean the difference between win and
lose (Figure 1). So how
can a pitcher throw a
pitch having unpredictable action in terms of the
path and the velocity?
Figure 1: The pitcher bears the most important role in a team when the team is
on defense.
Bernoulli’s principle—theory behind throwing a pitch
Before introducing the pitches, familiarizing ourselves with the theory behind it will allow us to have a better
understanding of the dynamics of
pitches. The motion of the pitch can be
explained by Bernoulli’s Principle,
which belongs to the field of fluid mechanics.
Bernoulli’s Principle states that for an
incompressible, non-viscous fluid un-
dergoing steady flow, the sum of the
pressure, the potential energy per unit
volume and the kinetic energy per
unit volume remains constant at any
point on a streamline1(Figure 2). The
meaning of compressibility and viscosity will be explained in detail in the
following part, ‘DoYou Know?’. The
principle can actually be derived from
the principle of conservation of energy, which states that energy cannot
be created or destroyed, but it is able
to change from one form to another,
and the total amount of energy in a
closed system is constant and will not
be changed1.
Bernoulli’s Principle is shown as follow,
P + ρν2 + ρgh
gh = constant
where P is the pressure acted by the fluid at any
arbitrary point
ρ is the density of the fluid
ν is the velocity of the fluid at a particular point
g is acceleration due to gravity
h is the height of that particular point above a
prepre-set reference level
Figure 2: Bernoulli’s Principle can also be written as P1 + ρν12 + ρgh1 = P2 + ρν22 + ρgh2
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Do you know?
Viscosity is an internal friction in a
fluid, always opposing the motion of
one part of fluid to another and there
will be energy loss if the fluid is viscous3. Generally, some sorts of fluids
like water that can flow readily usually
have a smaller viscosity than those that
are ‘thick’ such as oil3 (Figure 3).
For an incompressible fluid, the volume passing through a point
is the same at any time interval2. The
density of the fluid remains constant
regardless of the pressure2 (Figure 4).
Figure 4: Density of an incompressible fluid is a constant
Figure 3: Lava is a kind of fluid having high
viscosity. It flows slowly when its temperature is not high enough.
Let’s get back to baseball...
Fastball
straight.
Having the straightest path, fastball is
the fastest pitch among all kinds of
pitches4. It has no or minimal lateral
movement and is the most accurate
way to deliver a pitch4. To throw a
hard and straight fastball, the ball
should be held across over the horseshoe-shaped lace by the index and
middle fingers and should be thrown
over the top of the head, and backspin is produced by the fingertips
when the ball is released5 (Figure 5).
As the ball rotates with backspin, the
air near to the ball surface will move
in the same direction with the ball
surface, producing a circular air flow
around the surface of the ball6. This
circular flow assists the free air stream
flowing on the upper part of the ball
surface and opposes that flowing at
the bottom part of the ball, causing
the speed of the free stream flow of
the upper part bigger than that of the
lower part6. Therefore, the stream
flow at the top of the ball has a higher
kinetic energy than that at the bottom.
VOLUME 1, ISSUE 1
Figure 5 (left): To throw a fastball, the ball should
be held as loose as possible so as to prevent losing the energy of backspin transferred by the
hand of pitcher.
By Bernoulli’s Principle, the sum of the
pressure, the potential energy per unit
volume and the kinetic energy per
unit volume of the air stream at any
point should remain constant. Since
the potential energy per unit volume
is the same for the both upper and
lower part of the ball surface, the
pressure around the lower part of the
ball will be larger than that around
the upper part. The net pressure difference causes an upwards Magnus
force acting on the baseball, compensating the ball’s own weight acting
downwards7 (Figure 6). Hence, the
flight path of fastball is relatively
Figure 6: The Magnus force acting on the
ball causes a straight flight path.
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Let’s get back to baseball...
Curveball
opposite to the
fastball case. The
Curveball, usually with a lower speed
topspin acting on
relative to a fastball, is a kind of
the ball assists
breaking pitch, which means that the
the air stream
path of the ball will have a change on
flow at the top
its way to the plate. As the ball breaks
of the ball surdownwards when it nears the plate, it
face and opposes
is hard for a batter to hit the ball accuthe air stream
rately and usually results in the batter
flow at the botswinging above the ball's trajectory8
tom, causing a
(Figure 7).
kinetic
Figure 7: The path of curveball drops higher
dramatically on its way to the plate. energy at the upper part of the ball
The griping method is similar
and a lower kinetic energy at the botto that of a fastball, the only differtom part6.
ences are a deeper grip of the ball into
the palm, rolling the hand over the
top of the ball, and exerting topspin
By applying Bernoulli’s Principle, havby the index finger8. So the case is just
ing the same potential energy per unit
volume for the both parts, the pressure at the top becomes larger, producing a downwards pressure force
acting on the ball6. Thus, curveball
drops rapidly during its flight due to
the combination of the pressure force
and its own weight, which are both
acting in downwards direction 8
(Figure 8).
Figure 8: A downwards pressure
force acts on a curveball.
Conclusion
The above are only a simplified illustration of the principle of pitch. In fact, air is compressible. It has viscosity, although the
extent is low. Also, turbulence can exist in air flow. All these violate the assumptions of the Bernoulli’s Principle but the
Principle is still used to apply to it, since these only violate in a small extent and thus the deviation of the result predicted by
the Principle is negligible.
Science is in everywhere in our lives. It is hoped that students can be more aware to things around them. The more attention we pay to our lives, the more amazing things we can discover!
References
1.
Streeter VL. Fluid Mechanics, Example 3.5. New York: McGraw–Hill. 1966.
2.
Mok TM., Wong CS., Poh LY. New Way Physics for Advanced Level: Matter. Manhattan Press. 2005 (First Edition). 102p.
3.
Young HD., Freedman RA., Ford AL. Sears And Zemansky’s University Physics with Modern Physics. Hong Kong: Pearson Education. 2008
(Twelfth Edition). 473p.
4.
Charlotte RW. Under the Radar: A Professionally Unprofessional Blog for Pitchers - Dynamics of The 2 And 4 Seam Fastballs [internet]. 2009.
[cited 2010 Feb 10] Available from: http://woody20.blogspot.com/2009/12/gripping-baseball-2-seam-fastball.html Accessed: 2010 February10.
5.
Kaat J. Popular Mechanics: Baseball 2004 – Mechanics of The Fastball [internet]. 2004. [cited 2010 Feb 11] Available from: http://
baseball.about.com/gi/o.htm?zi=1/
XJ&zTi=1&sdn=baseball&cdn=sports&tm=12&gps=33_24_1259_655&f=10&su=p504.3.336.ip_&tt=29&bt=1&bts=1&zu=http % 3A//
www.popularmechanics.com/outdoors/sports/1283281.html%3Fpage%3D3
6.
National Aeronautics And Space Administration. Glenn Research Center - Curveball Aerodynamics [internet]. 2008. [cited 2010 Feb 18] Available from http://www.grc.nasa.gov/WWW/K-12/airplane/bball.html
7.
Kaat J. Popular Mechanics: The Mechanics of A Breaking Pitch
http://www.popularmechanics.com/outdoors/sports/1283161.html?page=4
8.
Anonymous. Curveball [internet]. 2008. [cited 2010 Feb 11] Available from: http://en.wikipedia.org/wiki/Curveball
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[internet]. 1997. [cited
2010 Feb 14] Available
from:
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