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Kinetic Energy

As an archer, you have probably heard the words 'kinetic energy' (KE) and wondered if it should matter to you. Many archers throw out the question of what is better: KE or speed. Knowing the equation and how physics works, I was thinking that considering each as separate factors was silly, as speed is the bigger part of the KE equation: KE = (1/2)Mass x Velocity squared

When I have asked other archers about kinetic energy, they always say just "use heavier arrows." A few years ago, I did an experiment where I shot every arrow I had at home and shot them through the chronograph. I used the speed along with a scale to calculate the kinetic energy, expecting the heavy arrows to have the most and the light arrows to have the least, they all had basically the same KE! WHAT?!

Then I started to calculate again. I know the light arrows have bounced off animals, probably due to bad shot placement. From this, I started to think about why heavier arrows are better. I found lots of websites, many where people argued that you should just be a man and shoot your 60-pound plus bow and forget about the numbers. And this probably is a good idea if you are just a big strong hunter and you want to shoot your heavy bow and heavy arrow and fly with it. But that doesn't work for me, at least not yet. It seems that thinner, heavy arrows have the least amount of drag, so since I'm not a man or have a 60 pound plus bow, I was intrigued by this idea of switching to a micro diameter arrow because, in theory, they will maintain their momentum (let’s call that penetration potential) and maybe make my pins be a little closer together(that's one of my important things to consider). I calculated the weight, ballistic coefficient, and momentum of those arrows at a few different draw weights. The values were only slightly better than the arrows that I already have. Except for the ballistic coefficient which was nearly 10% better, that means that it can fly 10% farther or loses 10% of its energy more slowly. Being at a lower draw weight and shorter arms puts me in a situation where all the little factors matter. Here is a table with some sample calculations that might be typical for a smaller woman:

After spending much time with arrows, speed, and KE, I have come up with two hunting combinations that I swear by along with their calculations for both of my bows.

I made one arrow that would fly faster for Sika deer hunting as they are skittish and I was concerned about jumping the string. While my heavier arrow is significantly slower, I have learned that with practice both shooting and arrow placement, that I am better with the slower arrows at a draw weight that I am comfortable with despite a larger pin gap. These heavier arrows penetrate better and are often some of the hardest arrows to pull from a foam target. After going to the heavier arrow, and working on my strength, I have increased my penetration on animals, which is really what we are all looking for.

- Jaimie Robinson, Huntress View Team Member

Follow Jaimie on Instagram at @mymomhunts.

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