I've pretty much come to the conclusion that KE is nothing more than a tool that bow manufacturers use to sell new bows. Kinetic energy, in a simplified formula is mass x velocity squared. So this formula leans more towards the speed of an arrow. When it comes to killing a deer, what I believe is far more important is momentum, which is mass x velocity. Why? because when you kill a deer you want the arrow to smash and break any bones, ie ribs, in the way of gettting to the heart lung area. That's why heavier arrows have more momentum, and penetrate further. The faster an object goes, the harder it has to hit in order to have the same penetration. That is why a rifle bullet will stop in a bucket of sand, but an arrow will go through.

The trade off of course is that a faster lighter arrow is more flat shooting, but it can also be louder. A heavier arrow will usually be quieter, but you have to aim higher to shoot farther, so to speak.

In the end, what matters most is shot placement. However, a heavier arrow will kill a deer better than a lighter arrow in my opinion.

Just my $.02. Would love to talk with a physicsguy about this,