There are few sports more exciting than playoff baseball, but behind every pitch there is also a fascinating story of physics. From gravity to spin, the science shaping the game can be just as compelling as the action on the field.
When the World Series returns to Toronto for Game 6, right-handed pitcher Kevin Gausman will take the mound. Gausman’s best pitch is the splitter, an off-speed pitch that looks like a conventional fastball but travels more slowly and drops more sharply before it crosses the plate.
Physicists consider the flight of a baseball as an example of projectile motion. The trajectory of the ball depends on several forces: the force of gravity (pulling the ball downwards), the drag force (slowing the ball as it moves through the air), and the Magnus force (which causes the ball to curve if it spins as it travels).
Why splitters are so hard to hit
So why is the splitter so difficult to hit? Start with speed. The average speed of Gausman’s fastball is 95 miles per hour (or 42.5 meters a second). Since the distance from the pitcher’s mound to home plate is 18.4 meters, this means that it takes 430 milliseconds, or less than half a second, for Gausman’s fastball to reach the batter.
In contrast, the splitter, which travels at an average speed of 85 mph (or 38.0 m/s), takes 490 milliseconds. That 60 millisecond-difference may seem small, but it can be enough to separate a strike from a base hit.
For context, a typical swing for a major league batter takes approximately 150 milliseconds. This includes time for the batter’s eye to form a picture of the ball leaving the pitcher’s hand, for their brain to process this information and send signals to the muscles in their arms, legs and torso, and for their muscles to respond and swing the bat.
This means a batter has roughly a quarter of a second to judge the trajectory of a pitch and decide whether to swing. Considering that it takes approximately 100 milliseconds for a blink of the human eye, it’s remarkable that batters can hit any major league pitch at all.
The importance of the drop
The second secret to the splitter is the drop. All baseball pitches drop as they travel towards home plate due to the force of gravity, which causes a baseball (or any object in freefall) to accelerate downwards.
If there were no other forces acting on the ball, this would cause Gausman’s fastball to drop by about 92 centimetres on the way to home plate, and his splitter to drop by approximately 115 centimetres.
In practice, however, there is another important force that acts on the ball to oppose the effect of gravity — the Magnus force. The Magnus force arises from the rotation or spin of an object (like a baseball) as it passes through a fluid (like air).
The ball’s rotation makes air move faster over one side than the other. On the side spinning in the same direction as the airflow, air speed increases; on the opposite side, it slows down. This difference in air speed creates a pressure imbalance, generating a force that acts perpendicular to the ball’s path.
This is an example of Bernoulli’s Principle, the same phenomenon that generates lift as air passes around the wing of an airplane.
In the case of a fastball, the pitcher creates a strong backspin by pulling back with their index and middle fingers as they release the ball. This rotation results in an upwards force, which causes the ball to drop far less than it would under the effect of gravity alone. The faster the rotation, the stronger this lift force becomes.
Gausman’s signature pitch
Gausman’s fastball typically drops 25 to 30 centimetres on the way to home plate — less than one third of the drop experienced by a “dead ball” without spin.
On the splitter, he changes his grip to dramatically reduce the amount of backspin, weakening the Magnus force and allowing the ball to fall much farther, about 50 to 75 centimetres, before it hits the plate. The result is a pitch that doesn’t reach the batter when or where they expect it to be.
As the Blue Jays edge closer to third World Series title — their first in 32 years — Gausman’s splitter offers an example of how physics can shape performance in elite sport. Understanding the science behind the pitch offers a new way to appreciate the game.
Patrick Clancy, Assistant Professor, Physics & Astronomy, McMaster University
This article is republished from The Conversation under a Creative Commons license. Read the original article.