What is Kinetic Energy?
The kinetic energy of an arrow is the energy it has based on its weight and speed and is measured in units of foot-pounds (ft-lbs). For example, an arrow weighing 350 grains and traveling at a speed of 275 fps would have 58.79 ft-lbs of energy. The best way to visualize this is if you shot your arrow vertically into an item weighing one pound it would have the energy to lift that item 58.79 feet.
Kinetic energy is important to archery hunting because it is one of the main factors in determining the penetration capabilities of your arrow. When an arrow is shot it immediately begins to lose velocity because of drag. As the velocity decreases, so will the kinetic energy. This means that your arrow will not have the same kinetic energy when it reaches a target at 40-yards as it does initially.