What is considered to be good kinetic energy for bowhunting? I ran some quick calculations and my bow seems to be shooting around 60.3 ft-lbs. I used the IBO Calculator page to figure it out.
25 ft. lbs. Small Game 25-41 ft. lbs. Medium Game (Deer, Antelope) 42-65 ft. lbs. Large Game (Elk, Black Bear, Boar) 65 ft. lbs. Big Game (Cape Buffalo, Grizzly) This is off of the Easton Archery website KE calculator page. Link: | Easton Archery Hope that answers your question.
I'm shooting in the upper 70s. Cape Buffalo, here I come! Sent from my iPhone using Tapatalk www.skyangler.com
I'm right around 52 but really don't pay that much attention to KE look more at momentum, it has more regards to penetration Sent from my iPad using Tapatalk HD
Momentum is very different and in this case kinetic energy is more desirable than momentum. Think of it like this: Would you rather get hit by a truck moving at 1 FPS or an arrow moving at 250+ FPS. The truck has a similar momentum as the arrow however the arrow has close to thousands times the amount of KE.
Momentum is what drives penetration, not KE. An arrow kill by penetrating and the head slicing/cutting, which is all driven by Momentum. KE is the bigger flashy number bow manufacturers spew, but it ls not what drives penetration.
They are both related. Let's break it down: Momentum = (Mass)*(Velocity) and Kinetic Energy = (Mass)*(Velocity Squared) If you are shooting a bow with a fixed draw weight and draw length, your speed does not change. That means that only the mass of your arrow can change. As Mass increases, both Kinetic Energy and Momentum increase. However If your mass is increasing, the velocity that the arrow is moving will go down. If your velocity decreases both Kinetic Energy and your Momentum decrease. BUT because Kinetic Energy is in terms of Velocity Squared it will go down faster. Therefore increasing your mass only get's you so far. It's a balance (aka a bell curve) and you'd have to do calculations on your own set up to see what the best mass would be to optimize both KE and Momentum. As for the blades opening: It takes energy to open the blades. Momentum helps keep the arrow moving, but the KE would be the main factor in opening a mechanical broad head. So in laymen's terms: Energy goes from bow to arrow, arrow to animal. KE will give you the best idea of performance, as it is very relatable. But you can't ignore Momentum. Also for the OP: You're energy's fine. *Note: I ignored dividing by 2 in the KE equation for simplicity's sake. Doesn't really make much difference as it's not a variable. Also I skipped over the relation from mass to velocity, so if you're confused on that I can explain. Or look it up yourself
All true, however you can have high KE numbers and still have poor penetration. Fast light arrows will look good on paper as far as KE numbers, however they are poor for penetration.
Agreed, hence why I said you can't ignore momentum. And why your mass is an optimization problem. There is no end-all-be-all number.
I honestly don't know. But why not figure it out? Use the above mentioned equation with your bow specs and let me know what your number is. However you're going to have to do some conversions to get the units correct. Let me work on an excel spreadsheet and get back to you.
There are actual momentum calculators online. Assuming that the data you put into them is accurate, the calculator should be as well.
I'd argue that broadhead selection is much more important than KE or momentum. You can setup anything with more than 45ish lbs of KE to penetrate sufficiently out to 30 yards if you are using the right arrow and broadhead.
I found a calculator online and it gave me about 76ke and .55 on momentum. I have no idea if thats a good or bad number and haven't really found much on the topic. I'm shooting a 456 grain arrow at 270 fps. Sent from my SCH-I545 using Tapatalk 4
What are the units on the Momentum number? The proshop I got my bow from, said my KE was about 68 ft-lb and my top speed was 270 ft/s. With those numbers and arrow weight (I don't remember exactly so I used 350 gr), my Momentum was 1.86 kg*m/s or .286 mcp. I have no idea what this second unit is and I can't seem to find it online, so we're just going to stick with the kg*m/s.
