But what else happens when the batter makes contact with a pitch? What factors
besides aerodynamic drag determine how far and how fast the ball will travel?
What makes one hit a home run, another a weak fly ball, another a hard grounder?
The first thing affecting a hit is the angle and location
of contact between the bat and the ball. There is a perfect location for
contact along the length of the bat, which batters refer to as the "sweet
spot," or "good wood." This is the point scientists call
the "center of percussion," the place on the bat which, when hit
by an impulse (the ball) produces no impulsive reaction at the point of
suspension (your hands holding the bat). When a hitter hits a ball at the
sweet spot, she feels no wobbling or twisting of the bat, and all of the
swing's power is transferred to the ball. On a baseball bat, the sweet spot
is usually located in the middle of a six-inch area around the maker's label,
extending up towards the tip of the bat. A hit outside of the sweet spot
results in vibration of the bat and a weak hit. It can even break the bat.
The vertical location of the contact matters too. The baseball is round,
and the bat is cylindrical, or barrel-shaped. If the batter's swing is off-center
by more than a few millimeters vertically, the hit will be a fly ball or
a grounder. A dead-center hit will be a line drive, and a hit a few millimeters
below center could be a home run. But it could also result in a deep fly
ball, easily caught for an out by the fielders. What's the difference? The
determining factor lies in the physical properties of the bat and the ball,
the moment of contact between bat and ball, and the interaction of the ball
with the air as the ball flies towards the outfield.