While most technical experts in the archery and firearms industries extol kinetic energy (KE) over momentum, there are still some that steadfastly believe momentum is much more important to an arrow’s lethality. Unlike KE, which measures an object’s total energy in motion regardless of direction, momentum is a measure of the persistence of an object’s forward movement – essentially its “resistance force” against stopping.
The physics behind this is actually quite simple, but there are some aspects that may seem counterintuitive to bowhunters. To understand the concept, it’s helpful to review the difference between potential energy and kinetic energy.
Potential energy is an object’s stored energy, and it exists because of the work that was done on it. An arrow sitting at rest in a quiver has no energy, so to give it energy work must be performed. That work is performed by the archer as he or she draws the bowstring and limbs back, and this energy is stored in the flexed bow limbs as the string is released.
Upon release, the potential energy is converted to kinetic energy (KE). The faster an arrow travels, the more KE it has, and the more likely it will penetrate deeply into an animal. During its flight, some of that kinetic energy is also converted to sound. This can give hunters a distinct advantage, as the loudness of the arrow’s impact is usually enough to surprise and startle target animals. The louder the arrow is, the less time it has to react and move, which greatly increases the odds of making a fatal impact.
