Who said that physics wasn't fun?
Kinetic energy is a wonderful thing. After all, it is one of the major contributors to job security for our beloved archery product engineers. As such, I read about it (KE) all the time. However, the physicist in me compels me to make an argument for another of our often-overlooked friends, momentum. Momentum is related to kinetic energy in that they are both functions of mass and velocity; KE = ½ mv2, where as momentum (denoted as p) p = mv. In the world of projectiles, it works kind of like this; KE gets the projectile to the target, momentum, on the other hand, drives the projectile into the target. In other words, momentum is the driving force behind the penetration of the projectile. Certainly there are a lot of variables that contribute to the penetration of any projectile, an arrow included (diameter, coefficient of friction between the shaft and the target, coefficient of friction between the broad head and the target, etc.). However, all things being equal, two projectiles, one with a greater mass strike a target with the same velocity. The lighter projectile will almost certainly have a greater KE (after all, velocity in the formula for kinetic energy is squared) when it reaches the target, but the more massive arrow will almost certainly have a greater momentum (due it its relatively large mass). As such the more massive arrow will penetrate the target farther than the light arrow. In a hunting situation the more massive arrow will have a greater probability of causing a fatal wound due to greater penetration!! Who said that physics wasn’t fun??!!