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Breaking Down Jennie Finch:
Does the Rise Ball Really Rise?

Jaclyn Parlo, Advisors: Donna Mullenax and Dr. Bill Baird

Abstract

The rise ball is a dominant pitch in fastpitch softball. The velocity and backwards rotation are two of the factors that play a role in causing the ball to actually rise. Video clippings of several skilled pitchers and a pitching machine will be used to study the flight of the ball. The overall data collected will determine if the rise ball actually rises above the trajectory path and "jumps" over home plate, or if it is merely an illusion to batters.

Background

For years, people tried to determine if a curveball (in baseball) curved and a fastball (in baseball) jumped at home plate. Through must research and debate, it has been shown that curveballs do in fact curve, but fastballs do not jump, but rather, fall slower than expected causing the hitter to perceive that the ball has risen.1 The motion of the fastball is due to its backward spin that produces a lower air pressure above the ball than below the ball. This difference in air pressure produces an upward lift on the ball. Thus the Bernoulli Principle goes into effect. Please note that the fastball does not rise though; it simply falls slower than a ball without a backward rotation.2

In 1853, Heinrich Gustav Magnus developed the concept of the Magnus Effect while at the University of Berlin.3 To simply explain the Magnus Effect: it is the force perpendicular to the spin axis and the direction of motion. For example, the Magnus Effect causes artillery shells to have a systematic shift.4 In fastpitch softball, the rise ball has the same type of rotation as the fastball. The motion of the rise ball is shown in Figure 1. The top of the ball is rotating toward the pitcher. Therefore, the force produced by the Magnus Effect is up, or in the opposite direction as the weight of the ball. For the rise ball to rise above its initial line of trajectory, the force due to the Magnus Effect must be greater than the softball's weight.

Many message boards on the Internet are full of debates between those that believe the rise ball rises and those that believe the rise of the rise ball is just an illusion as it is with the baseball.5 However, no research on the rise ball has been published. According to the coaches that have been interviewed and Mr. Ernie Parker, who has coached some of the best pitchers, no one has studied the physics behind the rise ball. On the message boards, those that say the ball cannot rise state a variety of reasons including: (1) the mass is too great, (2) the pitcher cannot get the ball to rotate with sufficient angular speed, and (3) the fastball does not rise, so the rise ball cannot either.

The aerodynamic forces acting on the softball are far from simple because of several reasons. The threads on the seams disturb the air. We will not go into great depth of the aerodynamics forces, but rather focus on the Magnus Force, Fm [pounds-force], which can be expressed as:

Fm = KfVCd

Where f is the spin frequency [rpm], V [mph] is the velocity of the softball, Cd is the drag coefficient, and K is a constant that has been estimated to be approximately 2E-6.1 If Fm is greater than W(=mg), then the ball will lift. It is our goal to determine if Fm is ever greater than W and then determine why.

magnus force

image 2
Figure 2: Path of JUGS LITE-FLITE® Softball using a pitching machine

This shows the path of the JUGS LITE-FLITE® Softball, which has one-third the mass (59.50 g) of a regulation softball (181.17 g). For this particular pitch, the machine, on the left, was set at 70 mph. The rise is apparent as the slope of the path increases.

image 3
Figure 3: Path of a Wilson (regulation) Softball using a pitching machine

For this particular pitch, the machine was set at 70 mph. The rise for the regulation softball is not as apparent as the rise of the JUGS LITE-FLITE® Softball. This is mostly due to the difference in mass, which results in a greater weight for the regulation softball.

image 4
Figure 4. Path of a regulation softball pitched by a person

Here we videotaped a pitcher while standing behind the catcher. The camera was near the height of the release point. Though this is not the optimal place to view a rise, it is the view that batters see. The yellow circles represent the ball at the first 6 frames the DVD Cam recorded. The distance between the circles increase. Therefore this leads us to believe that the ball is rising slightly above its initial trajectory.

Conclusion

According to Figure 2, the JUGS ball does rise above its path of trajectory. The rotation and velocity produce a force that is greater than the ball's weight, causing it to lift. Evidence proving that regulation softballs rise has yet to be proven. When studying these balls by means of a pitching machine slight lift was noticed, but not to the extent at which the JUGS ball rose. We are lead to believe that this is due to the fact that a pitching machine does not provide the resistance required to lift these heavier balls. Also, the absence of a high-speed, high-resolution camera hindered us from being able to break down a pitch thrown by a pitcher. Therefore, we are lead to believe that if we can get footage of a skilled pitcher who throws a rise ball with tight rotation, high velocity, and extreme resistance with this camera, then proof that a rise ball really rises about its trajectory path will be shown.

What is Next?

  1. Obtain a high-speed, high resolution camera to study the motion of the ball.
  2. Determine the mechanics of the rise ball.
  3. Determine the parameters at which the ball rises.

References

  1. Adair, Robert K., The Physics of Baseball, Perennial-Harper Collins Publishing, 2002
  2. Brancazio, P., The Physics of a Curveball, Popular Mechanics, 1997,174, 56-57
  3. Von Baeyer, H. C., Physika: Magnus on the Mound, The Sciences, 1986, 26, 7-8
  4. Fox, R. and A McDonald, Introduction to Fluid Mechanics, New York: Wiley, 1985, pp 481
  5. http://www.batspeed.com/messageboard/8609.html

All portions of these materials are copyright 2006 Armstrong Atlantic State University and AASU Physics.