Explaining a fastball's unexpected twist

November 18, 2018

WASHINGTON, D.C., November 18, 2018 -- An unexpected twist from a four-seam or a two-seam fastball can make the difference in a baseball team winning or losing the World Series. However, "some explanations regarding the different pitches are flat-out wrong," said Barton Smith, a professor of mechanical and aerospace engineering at Utah State University who considers himself a big fan of the game.

He and his doctoral student, Nazmus Sakib, are conducting experiments to explain how baseballs move. Sakib and Smith will present their findings at the American Physical Society's Division of Fluid Dynamics 71st Annual Meeting, which will take place Nov. 18-20 at the Georgia World Congress Center in Atlanta, Georgia.

A baseball is asymmetric owing to the figure-eight stitching pattern, and the way a baseball moves through the air depends on the degree and direction of its spin and its orientation when the hand releases it. The Magnus effect, or the force on a spinning object moving through a fluid like air, pushes in the direction that the front of the ball is spinning. So it causes a ball with topspin to drop and a ball with backspin to gain some lift -- enough to slow its fall, but not enough to overcome gravity.

This well-studied phenomenon affects most pitches except for the virtually spin-free knuckle ball, which is gripped with the thumb and fingertips. The two-seam fastball, which is gripped by the middle and index fingers along the seams, seemed to also behave in a way not explained by the Magnus effect.

Sakib and Smith focus on these two pitches, which are influenced by forces other than the Magnus effect. In their study, the researchers set up a pitching machine that hurls fastballs and knuckleballs through a smoky path. Automatic photographs, triggered by laser sensors, captured two images of the ball and smoke after release. Then, using a technique called particle image velocimetry, Sakib and Smith tracked the movements of the smoke particles to compute the velocity field around the ball and the direction of the rotating air at a given spot.

Then, they computed the "boundary layer separation" by identifying the portions of the ball's surface where the layer of air surrounding the ball had separated to form the wake. While the boundary layer separation varies differently for the two fastball pitches as the ball rotates, the net effect is the same.

Sakib and Smith found that the two-seam pitch has a tilted spin axis due to the fact that one finger leaves the seam before the other, which can cause the ball to move sideways, unlike a four-seam fastball. In the case of the knuckleball, the point of separation can change midflight, causing the ball to randomly shift directions.

Smith is now "hoping to meet a major league pitcher who wants to use what we've learned through fluid dynamics to throw a better pitch."

Presentation E17.1, "Velocity fields of pitched baseballs using Particle Image Velocimetry" by Nazmus Sakib and Barton Smith, will be Sunday, Nov. 18, 5:10 p.m. in Room B304 of the Georgia World Congress Center in Atlanta. Abstract: http://meetings.aps.org/Meeting/DFD18/Session/E17.1


Main meeting website: https://www.apsdfd2018.org/

Meeting technical program: http://meetings.aps.org/Meeting/DFD18/SessionIndex2

Invited talks: http://meetings.aps.org/Meeting/DFD18/APS_Invited

Hotel information: https://www.apsdfd2018.org/hotels/


At the Annual Meeting, The Gallery of Fluid Motion will consist of posters and videos submitted by attendees illustrating the science and beauty of fluid motion. More information can be found here: https://gfm.aps.org/.


We will grant free registration to credentialed journalists and professional freelance journalists. If you are a reporter and would like to attend, contact Rhys Leahy or the AIP Media Line (media@aip.org">media@aip.org">media@aip.org">media@aip.org, 301-209-3090). We can also help with setting up interviews and obtaining images, sound clips or background information.


A press briefing featuring a selection of newsworthy research will be webcast live from the conference Monday, Nov. 19. Times and topics to be announced. Members of the media should register in advance at http://apswebcasting.com/webcast/registration/aps1118.php.


The Division of Fluid Dynamics of the American Physical Society, established in 1947, exists for the advancement and diffusion of knowledge of the physics of fluids with special emphasis on the dynamical theories of the liquid, plastic and gaseous states of matter under all conditions of temperature and pressure. For more information about DFD, visit https://www.aps.org/units/dfd/.


The American Physical Society (APS) is a nonprofit membership organization working to advance and diffuse the knowledge of physics through its outstanding research journals, scientific meetings, and education, outreach, advocacy, and international activities. APS represents over 55,000 members, including physicists in academia, national laboratories, and industry in the United States and throughout the world. For more information about APS, visit https://www.aps.org/.

American Physical Society

Related Baseball Articles from Brightsurf:

Mortality rates of major league baseball players
Major league baseball (MLB) players had lower death rates overall and from many underlying causes of death compared with men in the general US population, differences that could be associated in part with the physical fitness required for their jobs.

Outcomes of non-operatively treated elbow ulnar in professional baseball players
Professional baseball players with a low-grade elbow injury that occurs on the humeral side of the elbow have a better chance of returning to throw and returning to play, and a lower risk of ulnar collateral ligament surgery than players who suffered more severe injuries on the ulnar side of the elbow.

NJIT mathematical sciences professor releases major league baseball predictions
NJIT Mathematical Sciences Professor and Associate Dean Bruce Bukiet has published his model's projections of how the standings should look at the end of Major League Baseball's regular season in 2019.

The short, tumultuous working life of a major league baseball pitcher
There are pitchers in Major League Baseball (MLB) who have had 30-year careers, but as UC Riverside demographer David Swanson points out, these are extreme outliers and often the stars of the game who receive most of the media's attention.

Why did home runs surge in baseball? Statistics provides twist on hot topic
Around the middle of the 2015 season, something odd started happening in Major League Baseball (MLB): Home runs surged.

For professional baseball players, faster hand-eye coordination linked to batting performance
Professional baseball players who score higher on a test of hand-eye coordination have better batting performance -- particularly in drawing walks and other measures of 'plate discipline,' reports a study in the July issue of Optometry and Vision Science, the official journal of the American Academy of Optometry.

For high school baseball pitchers, extra throws on game day add up but go uncounted
For high school baseball pitchers, limiting throws during a game helps to prevent fatigue and injuries.

Foul ball! Time to abolish rule protecting MLB from liability when fans are injured
In advance of Major League Baseball's opening day on Thursday, new research from Indiana University's Kelley School of Business suggests that the risk of fans being hit by a foul ball or errant bat at games has increased in recent years.

Vision, sensory and motor testing could predict best batters in baseball
Duke Health researchers found players with higher scores on computer-based vision and motor tasks had better on-base percentages, more walks and fewer strikeouts -- collectively referred to as plate discipline -- compared to their peers.

Review finds poor compliance with helmet use in baseball and softball
Despite lower rates of traumatic brain injuries in baseball and softball, there is poor compliance overall with helmet use and return-to-play guidelines following a concussion across all levels of play, according to a new systematic review.

Read More: Baseball News and Baseball Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.