“Crack!” A baseball bat makes solid contact with a baseball whizzing through the air at 93 mph, sending it flying into the outfield and over the fence. A home run! But what is really behind this classic American pastime? The answer: physics.
Junior Charlie Cowan said, “I think that understanding the physics behind everything is important. Being able to understand the way the moving world around you works is not only important but incredibly interesting.”
First, the pitch. What forces are acting on the ball? Friction, gravity, drag, and the Magnus effect–a phenomenon where a spinning object moves through a particular fluid. Without friction, the ball would simply slip from the pitcher’s hand. US Science Department Chair and US Physics Teacher Brian Potter-Racine said, “A pitcher could throw a ball without friction because they could cup the ball in his hand. However, if a pitcher did manage to release the ball, they would slide off in the opposite direction due to the lack of friction between their feet and the field.”
If a ball is not thrown fast enough, gravity will cause it to drop and not reach the plate. Although, of all forces, gravity is the least impactful. Drag, or air resistance, slows the ball down and increases the effects of gravity. However, this is typically not enough to have a large effect.
The final force, and the most important, is the Magnus effect, which results from the ball’s spin. “Pitchers rarely think about gravity and drag because of the Magnus effect, which is an aerodynamic force and is the primary force on the ball,” said Dr. Victor Lupi, Ph.D., an M.I.T. aerospace engineer.
If a pitcher adds topspin–spinning the ball forward–the ball’s flight path will drop, creating a “sinker.” Backspin is the opposite: the ball spins backward and “floats,” making it easier to hit.
The ideal type of spin is a sidespin. Sidespins cause the ball to curve right or left, creating what is known as a “curveball,” a pitch that senior first baseman Tommy Murphy says is “very common at every level of baseball.” Dr. Lupi said, “The spin rates can get very high, in excess of 1500 rpm.”
When a pitcher puts no spin on a ball, they create a “knuckleball.” Murphy said, “The knuckleball is one of the hardest pitches to throw.” A knuckleball appears to move randomly, so a batter does not know which way the ball will curve. The drag from the baseball’s seams causes this apparent randomness. The ball’s orientation upon its release determines which seams experience drag.
Physics also comes into play when batting. The key to batting is the elasticity in the collision between the ball and the bat. For example, if someone throws a lump of clay against the wall, it will splat. The collision has no elasticity because the energy from the lump of clay dissipates. The collision’s goal is to transfer all the energy from the bat into the ball.
To achieve maximum elasticity, a batter would need to hit the ball in the bat’s sweet spot, or center of percussion, which is generally about three-quarters down the bat toward the tip. If this does not happen, they will feel vibrations in their hands. These vibrations require energy themselves, therefore leaving less for the ball. When a batter properly hits a ball, almost nothing should be felt in the hands.
The other factor for achieving maximum elasticity is the bat’s material. Pro baseball bats are usually made out of hardwood. The harder the wood, the more elastic it is. Aluminum, which is typically used at the collegiate level and younger, is also extremely elastic. Both cause a lot of energy to be transmitted between the bat and the ball.
When a batter is striking a ball, they need to read the pitcher’s hand motion to anticipate the pitch. Murphy said, “If you are able to read spin, that’s massive, and it will give you an upper hand.”
If a batter manages to connect with a pitch, but swings too early or late, they would most likely hit a foul. Dr. Lupi said, “It’s really all about the timing. Whether the ball is spinning or not does not really affect what happens after you hit the ball.”
The ball’s speed, on the other hand, has a large effect on the ball strike. The faster the pitch comes in, the faster it goes out. Likewise, the swing speed affects the ball strike. If a batter needs to reach far, low, or high to hit a ball, they cannot transfer as much energy into the swing. Where the ball hits in the batter’s strike zone is important to maximize the amount of energy transferred.
Stay tuned for live-action baseball physics when the Shorecrest baseball season starts with its first home game on February 11, 2025.
