So in our collision between bat and ball, what has happened? Both objects experience an equal change in momentum as a result of the collision. But the greater mass of the bat means that, for a given change in momentum, it will experience a much smaller change in velocity than the ball. The much lighter ball undergoes a large change in velocity, which results in the ball flying into the outfield.

So it would appear that a large, heavy bat would be the best for hitting a ball a long way. However, a large, heavy object also requires a great deal of effort to accelerate it from a standstill. It has LOTS of inertia. (Inertia is the tendency of a still object to remain still, and a moving object to keep moving) A batter has only split-seconds in which she must to decide to swing and accelerate the bat to meet the ball. A heavy bat requires great strength and excellent reflexes to use, otherwise it becomes a liability. If the bat is too heavy, the pitch will pass by before the batter can hit it. Some professional hitters prefer relatively light bats, which they can accelerate and swing quickly and accurately.

Hitters have illegally altered bats to make them lighter, by drilling out the center of the bat and filling it with cork or another light material. Most hitters who use lighter bats are "contact" hitters, specializing in carefully placed base hits, instead of "swinging for the fences". However, a few light-bat hitters have managed to hit a lot of home runs; Hank Aaron broke Babe Ruth's lifetime record of 714 home runs. A hitter with quick wrists using a light bat can generate tremendous bat speed, thereby generating great momentum.