The Magnus Effect And Baseball

PITTSBURGH – In 1852, a German physicist by the name of Gustav Magnus was trying to figure out why spinning artillery shells sometimes curved in unpredictable ways.

What he discovered was that a sphere or cylinder spinning in a moving airstream develops a force at a right angle to the direction of the moving air and curves away from its principal flight path.

And with that, the Magnus Effect was born.

Fast forward nearly 170 years to present day, and we can still see how important the Magnus Effect is when observed and studied in sport, particularly such sports as baseball, golf, tennis and cricket, of which we will focus on baseball.

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When a baseball pitch is thrown, the ball is also spinning (what we know in the pitching lexicon as Spin Rate). Because the ball is spinning, it experiences a Magnus Effect (or Magnus Force).

This effect and/or force is largely responsible for the amount of curve or ‘break’ the baseball experiences as it is traveling to the catcher. 

Moreover, the effect is such that it greatly affects how much the ball tends to move in the direction that the leading edge is turning (what we know as Spin Direction, commonly referred to by a clock face … i.e. a ‘12 to 6 curveball).

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A proper curveball thrown with ‘12 ‘o clock to 6 ‘o clock’ spin creates a high pressure zone of air on top of the ball as it is traveling toward the catcher. This high pressure zone, in turn, helps deflect the ball downward in flight. 

So instead of counteracting gravity, the curveball actually adds additional downward force, thereby giving the ball an exaggerated drop in flight.

The unsteady top-to-bottom pressure difference on the ball aids gravity in forcing the ball toward the ground. The injected particles follow the instantaneous flow velocity and thus trace out the unsteady flow pattern behind the rotating baseball.

In addition, the particles follow a slightly upward path which indicates that the reaction force on the ball (due to the change in air flow momentum) is also toward the ground.

This combination of air pressure + gravitational pull is – in a nutshell – a simple way to look at, and understand the Magnus Effect. 

A fastball – diametrically opposite of the curveball – travels through the air with backspin. The backspin creates a higher pressure zone of air ahead of – and under – the baseball (in direct opposition to the curveball). 

Furthermore, the baseball’s seams augment the ball’s ability to develop a boundary layer between the ball and the air. Because of this, the effect of gravity is partially counteracted as the ball rides on – and into – increased air pressure as it zooms toward the catcher. 

Thus, the fastball falls less than the curveball.

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So, to recap….

The upward Magnus Effect – a fastball where the pitch has backspin – opposes gravity and keeps the ball in the air longer, whereas the downward Magnus Effect – a curveball where the pitch has topspin – helps aid gravity, and ultimately shortens the flight of the baseball.

Furthermore, the higher the spin rate, the more pronounced these variables are. 

A curveball thrown with a spin rate of 2,900 RPM’s (revolutions per minute) will break or drop much quicker and sharper than the same curveball thrown with a spin rate of 2,100 RPM’s. 

The same concept applies for a fastball, in terms of spin rate. 

The higher the spin rate, the less the ball falls (a fastball with a high spin rate is commonly referred to as a ‘rising fastball’ – a term that is used by baseball announcers, but actually cannot occur due to the laws of physics). 

At its core, the Magnus Effect is the aerodynamic force on a spinning baseball. The faster the ball spins, the larger the force.