Let's pause here for a word some of the things involved in any collision: momentum, and force. Momentum is a moving object's mass multiplied by its velocity.

Momentum= Mass * Velocity

A slow moving, heavy object has great momentum, as does a light, fast-moving 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

Rearranging a little gives us:

force * time interval = change in momentum

This equation tells us 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.)

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.

When a 30 oz. bat traveling 70 mph strikes the 5 oz. ball traveling 90 mph in the opposite direction, they remain in contact for about 2 milliseconds. What happens? Well, we know from experience that the ball ends up sailing towards the outfield at about 100 mph. But what happened in the collision?

There is a very important law in physics called the "conservation of momentum". This law states that there must be the same amount of momentum after the collision as there was before the collision. You have to add up ALL the momentum before and after. So in our case, you add up the bat+ball before, and that must equal bat+ball after. In this collision the bat slows down and gives much of its momentum to the baseball.