Revisiting the Magnus Effect

PITTSBURGH – A little over two weeks ago we looked at the Magnus Effect and how it applies to baseball. With the help of Dr. Rod Cross and Dr. Alan Nathan, we learned how air pressure and gravity affect the way a baseball spins and curves when pitched.

Today, we will revisit the Magnus Effect and look further into the specifics of how it affects both a curveball and a fastball.

The video at the top of this post shows the Magnus Effect, relative to how it affects a curveball.

The reason this video is placed at the top of this post is because the Magnus Effect has the most ‘influence’ on a curveball, in terms of the majority pitches that are thrown by a pitcher.

Here’s why:

A curveball thrown with topspin creates a higher pressure zone on top of the ball, which deflects the ball downward in flight. Instead of counteracting gravity, the curveball adds additional downward force, thereby giving the ball an exaggerated drop in flight.

In the image below, we can see that motion in action.

Magnus Force on a curveball

This is important to curveballs because as the ball moves forward, drag acts on the ball, slowing it down.

For a spinning ball, the stitches on the ball will cause pressure on one side to be less than on its opposite side. The Magnus Effect says stitches cause a higher velocity on one side than the other, and because of this imbalance in pressure, the air with higher pressure pushes the ball towards the side with less pressure, causing a curve.

As Dr. Nathan explains: “an overhand curveball (“12-6″) has topspin, so that the Magnus force is down, in the same direction as gravity. Such a pitch will drop more than it would from gravity alone.”

The fastball, on the other hand, travels through the air with backspin, which creates a higher pressure zone in the air ahead of and under the baseball. The baseball’s raised seams augment the ball’s ability to develop a boundary layer and therefore a greater differential of pressure between the upper and lower zones.

According to Dr. Nathan: “a baseball thrown with backspin (e.g., an overhand fastball) has an upward Magnus force, opposing gravity, so that a typical fastball does not drop as much as it would if it were solely under the influence of gravity.”

In his excellent piece in the Hardball Times on Freddy Garcia’s ‘mystery pitch’, Dr. Nathan explains the Magnus Force further:

The Magnus force is the aerodynamic force on a spinning baseball. Its magnitude is roughly proportional to the rotation rate of the baseball: The faster it spins, the larger the force. What about the direction? Well, the easiest way to remember the direction of the Magnus force is that it is always in the direction that the leading edge of the ball is turning. The leading edge is the side of the ball seen by the batter. As an example, a typical four-seam fastball is thrown with backspin, so the leading edge of the ball is turning up, and the Magnus force is upward, opposing gravity. The force of gravity is still larger than the Magnus force, so the net vertical movement is downward but less than it would have been with gravity alone.”

Below we can see effect that in action:

Magnus Force on a fastball

For further reading on pitch spin and spin rate, Dr. Nathan’s piece, “All Spin Is Not Alike” discusses magnus force and the vector nature of pitch spin as well as his research paper entitled, “The Effect of Spin on the Flight of a Baseball”.