How To Hit Home Runs

In the November issue of the American Journal of Physics, Gregory Sawicki, a UC Davis graduate student now at the University of Michigan, UC Davis mechanical engineering professor Mont Hubbard and William Stronge, a professor of engineering at the University of Cambridge, England, show what makes the ball fly farthest when it comes off the bat.

The study turned up some surprises. Popular wisdom says you can hit a fastball further than a curve ball, but it turns out the opposite is true, Hubbard said.

That's due to the spin of the ball. Curve balls are thrown with topspin so the top of the ball rotates in the direction of flight. When hit by the bat and thrown into reverse, curve balls automatically have backspin which gives them lift and carries them further. Fastballs are thrown out with backspin, so they spin the other way when hit, have less lift and sink faster.

To generate more backspin, the batter should hit the ball a bit below the center, although it's unlikely batters have much time to think about that, Hubbard said.

The study was prompted by longtime UC Davis baseball coach Phil Swimley, now retired, who asked Hubbard if he could work out whether rolling the wrists during batting was useful. It turns out to have very little effect, Hubbard said. Nor does using an aluminum rather than a wooden bat.

The most important factor in hitting a homer was the speed of the bat when it hits the ball, Hubbard said. The faster, the better.

Hubbard says studying the physics behind baseball gives him a stronger appreciation of the instinctive skills of great batters.

"How they do it with so much power and so quickly is amazing," he said.