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 by the fielders for an out. What's the
difference? The determining factor lies in the physical properties of
the bat and the ball, the moment of contact between the bat and the ball,
and the interaction of the ball with the air as the ball flies towards
Let's pause here for a word about some of the elements involved in any
collision: momentum and force.
Momentum is a moving object's mass multiplied by its velocity: Momentum
= Mass x Velocity
So a slow-moving, heavy object has great momentum, as does a fast-moving,
The next question to look at in a collision between bat and ball is the
question of force.
To slow any moving object (like a pitched ball), one has to apply a retarding
force to slow it down. The net force required depends on how much you
want to change the momentum and how quickly you want to change it. The
quicker the change, the greater the force. In other words:
Force = Change in momentum/Time
to change momentum
Force x Time interval = Change
This equation tells us that we have a balancing act. To cause a given
change in momentum you can apply a LARGE force for a short time interval,
or you could apply a SMALL force for a long time (or anything in between,
as long as the two multiply to the same number).
This means that you could stop a rolling car with your little finger,
if you could push against the car for a long time. You could even stop
the Queen Mary by breathing on it . . . for a VERY long time.
However, to effect a similar
change in momentum over a very short time would require a much larger
force. In real-world terms, this means that it takes A LOT of force
to stop a heavy, fast moving object quickly.