MadSci Network: Physics

Re: Does the mass of a person transfer energy to a batted ball.

Date: Thu Dec 3 07:59:12 1998
Posted By: Tom Cull, Staff, Clinical Sciences MR Division, Picker International
Area of science: Physics
ID: 911356424.Ph

Hi Kevin,

The quick answer to this question is that the mass of the batter has an undetermined effect on the power generated. Hitting instructors, players, coaches of all levels, fans, and scientists have been contemplating this since the dawn of baseball.

One can observe that in general power hitters are big guys like Mark McGwire, Sammy Sosa, or Mo Vaughn. But some power hitters are guys who throw everything into the swing like Reggie Jackson, Babe Ruth, or Darryl Strawberry. And some big guys are simply not power hitters. And the best MLB home run hitter of all time Hank Aaron was hardly a big burly guy.

I turn to my baseball physics bible The Physics of Baseball by Addair.

There are so many components to a baseball swing that keeping everything else equal is very nearly impossible. It is evident that the power of most swings is generated in the big muscles of the legs and back. The effect of the strength of the legs can be witnessed in the swings of guys like Jim Thome and Manny Ramirez who have a classic stride when hitting and make contact with a straight front leg and a bent back leg on their long home run balls. While other players have great power with very compact swings that seem to be all a matter of timing and bat speed like Kenny Griffey Jr.

Three "models" of a baseball swing are considered in the book: constant bat and batter total energy, constant batter and bat power, and constant kinetic energy of just the bat. This is power in the physics definition of the word: energy per unit time.

The constant kinetic energy of the bat model is pretty good for a simple approach to the physics of golf (a whole other topic I really like), but is not very good for a baseball and bat collision.

The constant bat and batter energy model is simple conservation of energy. Conservation of energy is how physics begin 99% of problems. This model tends to make the mass of a batter very significant because the baseball swing begins with the forward motion of the batter as he steps into the pitch. This step is kinetic energy 0.5MV2 where M is the mass of the batter and V is his speed. A bigger batter means more energy to the swing. Unfortunately this simple model does not work in the real case of a baseball swing.

The constant bat and batter total power is considered by Addair to be closest to correct. It considers the mass of the batter because the power generated is assumed to be related to muscle strength which in turn is related to mass.

My conclusion is that batter mass has less of an effect than ability to hit the ball properly. Swinging for the fences invariably has the effect of hitting for a lower average and producing more strike outs. Power hitting is all about bat speed. If you truly can hold all other things equal a stronger batter should be able to generate more bat speed and will tend to hit home runs farther than a lighter, slower swinging batter. In a home run derby, I would bet on Mark McGwire (big and strong) over Omar Vizquel (not-so-big). But who is going to hit more home runs in a battle between Mark McGwire and Ken Griffey Jr. is anyone's guess.


Tom "Warning Track Power" Cull

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