WVU experts explain the physics of baseball ahead of MLB return

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MORGANTOWN, W.Va. – Major League Baseball (MLB) is set to return July 23, and two astrophysicists at West Virginia University want to give fans a better understanding of how baseball and physics are connected.

D.J. Pisano, Chair and Professor of WVU Department of Physics and Astronomy and Associate Professor Sean McWilliams created a four and a half minute long video explaining how many parts of the game simply come down to physics.

Pisano is a Chicago White Sox fan and McWilliams a Philadelphia Phillies fan. One of the topics covered in their video was how physics factors when trying to hit a home run.

When the bat collides with a ball, you are transferring the momentum (the product of mass times velocity) from the bat to the ball. To maximize the momentum of the bat, you can either increase the mass of the bat or swing the bat faster. The speed which you can swing a bat, however, depends not on the actual mass of the bat but on its ‘swing weight,’ or moment of inertia.

D.J. Pisano – Chair & professor of WVU Department of Physics and Astronomy

Pisano even said that physics also factors in when deciding whether to use solid wood or an aluminum bat. In MLB players are not allowed to use metal bats, but in college and high school baseball, where they can, it may be worth understanding the physics.

The average major league baseball player will swing a bat at about 60 mph, Pisano said. With a solid wood bat, there is relatively little compression and a ball pitched at 90 mph will bounce off with an exit velocity of 90 mph. An aluminum bat, however, is hollow and can exhibit a larger trampoline effect, sending the same ball out with an exit velocity closer to 100 mph.

McWilliams said the flight of a baseball, in particular, is really just fundamental physics, fluid dynamics, hydrodynamics, all of which are topics that students learn in the classroom.

When a pitcher throws a baseball, McWilliams said, if they just throw an ordinary baseball, the baseball will rotate with a backward spin and gravity will make the ball drop by a certain amount, so what the pitcher can do is they can put a different spin on the ball. He said one option is to spin the ball the other way, using a forward spin, rolling over the top of itself and what happens is the pressure on one side of the ball is lower than the other side so it pushes air in that direction.

There is a law of physics, Newton’s Third Law, saying if I push something one way I have to move another way, so the ball will move in the opposite direction. With the curveball it would drop more than it would just under gravity and so the bat is expecting the ball to come along a certain flight and it drops more than the pitcher can put sideways spin or any combination of these things and the ball will dance around in different ways depending on what the pitcher is doing. And that’s all just fluid dynamics of the surface of the ball interacting with the air that it passes through, it’s really the same physics as what makes an airplane takes flight. As a wing cuts through the air, there’s a longer path of flight under the wing than above and that causes lift, so it’s really the same thing.

Sean McWilliams – Associate professor, WVU Department of Physics and Astronomy

When he’s just watching a baseball game, especially live at the stadium, McWilliams said he will just relax and watch without thinking about the physics of the game. However, when he’s at home and can see the ball slowed down and tracked using cameras and modern technology he often thinks more about the physics of it all.

“A particular pitcher will throw a pitch and there’s a pitch called a knuckleball that doesn’t spin at all,” McWilliams said. “When I say the pitch dances, it will literally dive this way and then change direction and go the other way. It’s just fascinating to me as a physicist to understand exactly how that’s happening and how hard it must be for a major league hitter to try and adjust and do anything with that. It will pop into my mind here and there, but mostly I’m just watching, I just love the sport.”

All these elements of physics that go into the game could be overwhelming for batters to think about when they step up to the plate, so much so that it could hinder their performance, McWilliams said.

However, there is a growing field of sports science that’s starting to get attention and it focuses on tailoring the way players practice to include certain aspects of their swing and motion based on an assessment of the physics.

He said there is also a focus on how the body moves and different questions are asked to see how to get the most efficient movement. Questions like how do a pitcher’s arm and body move, how does the batter rotate, hips versus arms, versus wrists and what’s the optimal combination of things that are going to send the ball as far as possible, or propel the ball as fast as possible?

“I think that would be a dream to have the Phillies bring someone like me into to talk me about that, I think it could be interesting for them,” McWilliams said. “But there are people who are trained day in and day out to work on these sort of things, to have the players optimize their performance.”

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