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 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 the outfield.



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, light object.

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

or

Force x Time interval = Change in momentum

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.

	For more on the physics of hitting visit our interactive exhibit, "Scientific Slugger "!

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.