# Easy way to figure Kinetic Energy from arrow for peneatration for hunting



## Daniel Boone (May 31, 2002)

Click on this link


http://www.bowhuntinginfo.com/KineticEnergyNew.htm


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## geneinidaho (Feb 9, 2004)

*Db*

Thanks for the info. Here's another;


http://www.eastonarchery.com/downloads/programs/ShaftSelector2005/setup.exe


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## all4bows (Dec 6, 2004)

*Ke*

You can multiply speedxspeedxarrow weight and divide by 450240. If you can do that in your head, you can really impress your archery buddies!


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## johnhames (Apr 9, 2003)

KE really has no relation to penetration for hunting or anything else as per Dr Ed Ashby's resurch and paper, link found below:


http://www.bowhunters.org.au/bulletin.htm

Its time to put KE in the bucket of old wives tails and focus on momentum.


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## Chief P (Dec 1, 2003)

johnhames said:


> KE really has no relation to penetration for hunting or anything else as per Dr Ed Ashby's resurch and paper, link found below:
> 
> Its time to put KE in the bucket of old wives tails and focus on momentum.


If it has 'no relation to penetration' how do you get penatration without it. A broadhead WITHOUT KE is a broadhead that's not moving. So in your statement the speed and or weight of an arrow has no relationship to penatration.

KE is not an old wifes tale.


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## Bobmuley (Jan 14, 2004)

Chief P said:


> If it has 'no relation to penetration' how do you get penatration without it. A broadhead WITHOUT KE is a broadhead that's not moving. So in your statement the speed and or weight of an arrow has no relationship to penatration.
> 
> KE is not an old wifes tale.


Chief, What Asbuys paper stated is that KE isn't directly indicative of penetration potential...as it isn't a linear relationship. Momentum was given as the preferred method for determining the penetration potential (linear relationship). 

In other words two arrows with identical exterior characteristics and the same KE, but with different momentums don't have the same penetration potential. Two arrows with the same exterior characteristics and momentum, but different KEs do have the same penetration potential.

At least that's what I got out of the paper. :teeth:


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## Chief P (Dec 1, 2003)

Okay, I answered first then read it. I see where he is coming from. But with the equipment we are using now I don't see it a big deal unless you are shooting around 50lbs with a short draw.

One thing I found odd about his report. He says the number one reason for lost or wounded animals is poor penetration. Hard to believe. I would think poor shot placement would be number one.

I also believe KE has a place, most people know what it is and understand it better than momentum. It's one of those things, it's wrong but everyone uses it that way.


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## johnhames (Apr 9, 2003)

Chief P said:


> I also believe KE has a place, most people know what it is and understand it better than momentum. It's one of those things, it's wrong but everyone uses it that way.


Chief, This part is exactly right. It needs to be changed but I'm not sure how. I contacted Gold and asked them to include a Momentun chart with the KE one. --- No response. 

Fact is, KE can be increased and if done the wrong way the penetration can be lessened. That's probably a shock to the system of most folks on AT. It was for me. I know just a little physics and have a math degree, both of which lead me to believe Dr Ashby's analysis was correct. I only cringed when he mentioned the "ethical" shot on page 15. Fortunately it wasn't an important part of the discussion.


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## Bobmuley (Jan 14, 2004)

Chief P said:


> Okay, I answered first then read it. I see where he is coming from. But with the equipment we are using now I don't see it a big deal unless you are shooting around 50lbs with a short draw.
> 
> One thing I found odd about his report. He says the number one reason for lost or wounded animals is poor penetration. Hard to believe. I would think poor shot placement would be number one.
> 
> I also believe KE has a place, most people know what it is and understand it better than momentum. It's one of those things, it's wrong but everyone uses it that way.


Chief, I believe most of the research was done in Africa....penetration is more an issue on animals larger than whitetails, like elk-size game. I also think that as our hunters average age increases you're more likely to find bowhunters shooting around 50 lbs, plus more women and kids, and lets not forget the trad guys. 

Penetration could probably be directly linked to shot placement if I had to make a guess at it, but what if you could get more penetration on a not-so-good shot....that would be better IMO.

KE is useful to determine if our bow is efficiently transfering energy to the arrow. MO lets us know how the arrow will perform. 

Lots of bowhunters don't consider the whole system. Get a 2" cutting diameter head, slap 'em on the fastest arrow they can get from a 50ftlb bow and wonder (on occasion) why they didn't pass through a 250 lb buck at 40 yards. It'll work in alot of instances, but they fail to plan on the worst-case scenario that they'd still take the shot in. I say prepare for the worst, and hope for the best. Like a boy scout.


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## oldad (Mar 16, 2005)

*wHAT ABOUT HOGS?*

Aperantly this guy has never been hog hunting or spoken to hog hunters.You need lots of KE to get good penetration AND pass throughs.Leniar my butt!KE is what gets through thick hide and dense bones.L et alone the plate on a large boar.


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## johnhames (Apr 9, 2003)

oldad said:


> Aperantly this guy has never been hog hunting or spoken to hog hunters.You need lots of KE to get good penetration AND pass throughs.Leniar my butt!KE is what gets through thick hide and dense bones.L et alone the plate on a large boar.


Sure can't argue with you there, oldad. After reading the paper, where do you think he went wrong?


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## Bobmuley (Jan 14, 2004)

> Aperantly this guy has never been hog hunting or spoken to hog hunters.You need lots of KE to get good penetration AND pass throughs.Leniar my butt!KE is what gets through thick hide and dense bones.L et alone the plate on a large boar.


 Well, maybe not the hogs you're used to. But rather, warthog, hippos, rhinos, cape buffalo, a gizzillion kinds of antelope, crocodiles, elephants, etc. I'm pretty sure you're the hog expert.  You think its the KE because that's what you've heard you whole bowhunting career and its something that is easily measured and calculated.

Would you shoot a hog with a 100 grain arrow?


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## oldad (Mar 16, 2005)

*Ke*

Living in Texas for 51 years a pearson can easly hunt all year and I have. I quit counting all the hogs I have whacked 2 years ago bit it does number in the hundreds.I have more than my share of nalgi,whitetail,rams and other stuff with 4 legs as bow kills. None of them compare to a big wild hog after bieng shot with a bow.I have been selfemployed in the valve industry for 29 yrs. I should have enough common sense to understand energy in motion.The more ke you have the easyer it will be to get a pass through on those big animals at not so perfect angles.No I have not been to Africa, but me and my Allegance will be going soon.


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## Bobmuley (Jan 14, 2004)

oldad said:


> I should have enough common sense to understand energy in motion.


You said it yourself Oldad, "energy in motion"....momentum. We've been taught to use KE and it has been a easy value to assign to our arrows.

But, do you believe that a 100 grain 60 ftlb KE arrow is equal to a 600 grain 60ftlb KE arrow. I'd be willing to bet that you don't. I know that most of us shoot somewhere in the middle of those two weights and with good shot placement they'd both probably would work...even on hogs. As an example I've seen elk killed with everything from 280 grain arrows to 800+ grains. Neither would be my choice, but both proved themselves effective for those shots.

And, did you read the Ashby report? I bet your on the same side and don't know it. What you're likely calling KE is actually momentum (energy in motion).


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## DwayneR (Feb 23, 2004)

Something to think about....

When you pull back that bow of yours, you have potential energy...PE.
When you let go of that string, PE coverts to KE.
As that arrow flies, Momentum and KE are in play.

Lets take a example:
a bow that has 60 pounds of pull, shoots a arrow at 200 FPS.

Lets say that bow has a set potential amount of energy just before you let go.

When you let go, The KE is the EXACT same thing whether you use a light arrow, or a heavy arrow. The Momentum is ALSO the Exact same thing whether you use a Light arrow, or a heavy Arrow.

If ANY of these vary, it is because the Energy your limbs are holding, are not getting transfered to the arrow in the most efficient manner. That energy is loss through Vibration, Through drag, and through other various ways. This usually happens on the "lighter" arrows....But does not amount to anything significant to think about.

Now as that arrow leaves your bow, KE and MO will change. A very light arrow will slow down MUCH quicker than a heavier arrow. Thus the Momentum will drop off a lighter arrow quicker than a heavier arrow. Thus the big argument of "MO is more important than KE". Thus ALSO the argument of HEAVY arrows are better penetration than LIGHT arrows. (because the light arrows will bleed off MO quicker than heavier arrows).

Now with ALL of this said...Lets look at the facts of life... Most bows of today, are so darn powerful, that MO / KE is not even a small factor to look at. My bow produces 50 FPS ... Yeah that is not ALOT with todays bows, but 50 FPS blows through my deer and sticks itself into trees, to where I have to unscrew my arrow and use a broadhead puller. Now, lets look at the OTHER side of the coin...Recurves. My Mamba is 45 pounds, shoots a 530 grain arrow at a whooping 145 FPS, generating a KE of 25. Mechanical heads take 5 KE of energy to open... that leaves me 20 FPS of KE to kill a deer. Unless it is a PERFECT shot with NO RIBS, I cannot kill a deer. But instead, I must use a Cut On Contact broadhead. That broadhead does a wonderful job of slicing right through that deer. Not a passthrough...But pretty close! I Have a choice of a 325 grain arrow With 25FP or a 530 grain arrow with 25FP. But I also know, that the heavier arrow will not lose NEAR as much MO at 20 yards too! It will also not lose near as much KE. But for my setup, which is more ethical?? siding with the best KE/MO by using a heavier arrow? or siding with a smaller amount if KE/MO by using a much lighter arrow? They are all shot from the exact same bow. My ethical shot is a Cut on contact with a heavier arrow for my best penetration and humane kill. But for my other setup??? Who cares...at 50FP, the arrows plow through anything...

Dwayne


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## Jabwa (Dec 10, 2004)

Dr. Ashby's article was very enlightening! If I understand things correctly, we need balance arrow weight and speed against our greatest need- Arrow weight being more important for penetration, but speed being more important for correct arrow placement at longer distances. To me, this means large animals need to be hunted at close range with heavy and necessarily slow arrows, while smaller animals, such as mule deer or antelope, which may require a long shot, should be hunted with relatively lightweight, fast arrows. 

Hmmmm. Sounds right to me.

So why do the whitetail hunters want to pull a bow that shoots a 300 gr arrow 320 fps? Sounds like the Bow Manufacturers have done a K.E. marketing miracle to me!


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## Jabwa (Dec 10, 2004)

DwayneR:

Agreed. But how about a Moose at 50 yards? Still want to use that light, fast arrow?


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## oldad (Mar 16, 2005)

*I agree*

After I stoped my post I realized we are all talking about the same thing.Yes I did read the article.I soon realized that the writer was spliting hairsand it seemed to me he had no comon sense as to aplication in the hunting world.Guess I get a little nervy with technowannabe enginers, I have too deal with them all the time.


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## Bobmuley (Jan 14, 2004)

DwayneR said:


> Who cares...at 50Foot-Pounds, the arrows plow through anything...


...anything (?), and with any head? Is that your elk hunting setup? Is that what you'd take on a cape buffalo hunt? How about a Kodiak hunt? There is other game besides whitetails. 

I guess I've always liked knowing that I have the energy to penetrate from stem to stern. Or to go through the occasional shoulder blade if the buck/bull jumps or flinches. I don't need to change anything if I want to go moose or brown bear hunting. I don't do it at the cost of excessive noise or vibration. My motto has been to shoot heavy arrows fast....can't go wrong. :shade: 

To me I've always figured I could effect more tissue not by going to large heads but by increasing the depth of cut and insuring an exit hole for better blood trails. Its not a matter dead, but of ease of recovery for me (which is generally a non-issue, but I like to hedge my bets).

Oldad, I thought so. He is splitting hairs, but I think for the better. We've been discussing the light vs. heavy arrow thing for as long as I can remember and the light guys always say they have just as much KE as the heavy arrow guys, but their performance rarely is equal on tough/large game. Dr. Ashby's paper could be a great resource if we bowhunters could at least learn to use the right terminology.


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## oldad (Mar 16, 2005)

*What the heck*

What the heck! This fall when it cools down, why not everyone come to Houston to whack some hogs.It is a great way to practice your sneakin likean indian skills.Just north of town theres a pay to hunt place.(cogarrunranch.com)They usually keep about 175 pigs on the place and its no cakewalk either. You gotta work for them,IE ... walk ur legs off!Sorry about my speling, only made c in english.


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## Bobmuley (Jan 14, 2004)

Oldad...I would, but I'll be busy elk/bear/antelope/deer and hopefully moose bustin'. 

Pig huntin' for me is in May! though its happening in a much cooler place than Houston. :shade: Houston is too hot for me, and in the fall there's a chance of hurricanes.....I don't do hurricanes.  :smile:


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## johnhames (Apr 9, 2003)

The problem I'm having with this paper is that the conclusion reached on page 11 suggests two arrows with the same momentum don't necessarily have the same prediction for penetration. Instead the one having achieved the greater portion of its momentum from weight will penetrate further. It follows from this that momentum is not a good predictor of penetration and until we include the amount of momentum resulting from weight in some other defined calculation, there is still no linear predictor of penetration. It would be nice if one calculation would indicate just how effective in penetrating an arrow would be. I'll just keep shooting those 670-grains guys and see how it works out


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## oldad (Mar 16, 2005)

*Heavy arrows fast*

You sir are 110% right! If every archer shot with our idea there would be less game lost and the bow hunting world would be the better for it. Heavy arrows faster should be shouted from the roof tops!


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## oldad (Mar 16, 2005)

*Exactly*

Johnjames,
See what I mean about technogeeks? They always leave big holes in their thearys for those of us who have on the ground experince.
Heavy arrows pushed as fast as your body and bow can put out. It is as simple as that.
Hurricanes? They only show up July thru Sept. Fall is in late Oct. IT dosent cool off till then.Hurricanes? naw just a wee breeze.


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## Bobmuley (Jan 14, 2004)

johnhames said:


> It follows from this that momentum is not a good predictor of penetration and until we include the amount of momentum resulting from weight in some other defined calculation, there is still no linear predictor of penetration.


 John, going back and rereading I see what you mean and I misquoted. 

Momentum is not linear, but KE was reported as irrelevant to penetration potential. So, I say Momentum (and I assume you agree) is the more important of the two.

Maybe some momentum/weight ratio?



> They only show up July thru Sept.


 Is that state law or something  I distinctly remember flying in and out of Houston during one of your September breezes. I don't do breezes like that anymore.


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## oldad (Mar 16, 2005)

*You Are On To Something*

Momentum/weight ratio. That makes more sense for those who want to split hairs. Why not start a new standard? It is still energy in motion.


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## johnhames (Apr 9, 2003)

Bobmuley said:


> Momentum is not linear, but KE was reported as irrelevant to penetration potential. So, I say Momentum (and I assume you agree) is the more important of the two.
> Maybe some momentum/weight ratio?



Definitely momentum (MV) is more important than KE. But with the M being more important, there is still no index for penetration. Because there isn't one, it will be really hard to separate people from believing KE is the be-all end-all to penetration. 

With sights I think I would start with the maximum trajectory I could accept within ranges I could shoot. Then select the heaviest arrow within the spine range of the poundage I was able draw. 

I shoot instinctive so I choose the max bow poundage my body could take and completely control the shot. Then matched the spine to the bow and choose the heaviest weight arrow in the category and just dealt with the trajectory. My body squawks about the weight from time to time so I shoot 3 times a week year around and that forces a familiarity with the trajectory. It all works out.


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## johnhames (Apr 9, 2003)

oldad said:


> Momentum/weight ratio. That makes more sense for those who want to split hairs. Why not start a new standard? It is still energy in motion.


Since momemtum is mass(weight) times velocity. Momemtum/weight ratio would just give us velocity, right? But, yea a new standard is what we need.


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## oldad (Mar 16, 2005)

*Ratio?*

momentum times momentum times arrow weight diveded by 450240 ??
Hope I didnt start a new thread.


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## johnhames (Apr 9, 2003)

oldad said:


> momentum times momentum times arrow weight diveded by 450240 ??
> Hope I didnt start a new thread.


(mv)(mv)(m)/450240 --- velocity times M(squared) times a constant? How about (mv) squared? It adds m emphisis without cubing m. I guess I was looking for an expression with a definition in physics. Maybe that's not necessary.


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## oldad (Mar 16, 2005)

*You may be on to something*

Good idea! Why not present the problem as you see it with your formula to a physics prof. As oposed to speed/speed/arrow wt.divided by 450240
Might be a fun exercise for someone.


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## Jabwa (Dec 10, 2004)

BobMuley:

"My motto has been shoot heavy arrows fast. Can't go wrong." Don't you have shoulder problems? I never pull more than 65# and I can still do it at 62! Food for thought!


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## Bobmuley (Jan 14, 2004)

Unfortunately I don't really see an "easy" expression for penetration potential. You'd need coefficients for different broadheads (diameter, blade thickness, number of blades, ferrule diameter and shape, etc), drag coefficients for different shaft diameters and materials, figures for momentum (and how that momentum was derived), and the hardest to track down of all would be arrow tune/flight. 

While I agree momentum is better, its easy to see how we end up using KE to express our "potential".

Yes, Jim/Jabwa I have shoulder problems (both), I've had the same problem since I was 18 (23 years ago) playing baseball. In other words...wasn't caused by archery, of course it doesn't make it any better either.


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## Jabwa (Dec 10, 2004)

Yeah, yeah! And my knee and foot problems aren't caused from running marathons!  See you at Salida! By the way, we can use 10X binos this year.


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## johnhames (Apr 9, 2003)

> While I agree momentum is better, its easy to see how we end up using KE to express our "potential".


It's probably time to work on my form and avoid this topic's potential brain sprain. What has been working will probably keep working and that's momentum enough.


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## HNSB (Jul 1, 2004)

Just grip it & rip it! (or something catchy like that, but more appropriate to archery...)

I think some people put waaaayyyyyyy too much time into worrying about this stuff, whether you call it KE or momentum or whatever... (Inertia will be next?)


Not that I don't think it's interesting discussion, because it is... Just that even the largest game on the planet has been taken with arrows from both extremes. Heavy and slow... light and fast...

Grip it & rip it.

:beer: :shade:


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## Jabwa (Dec 10, 2004)

Really? Elephants with "light and fast"? Hmmmm.


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## DwayneR (Feb 23, 2004)

Hello Jabwa,

Jabwa>>Agreed. But how about a Moose at 50 yards? Still want to use that light, fast arrow?<<

<chuckle> Nope...my lightest arrow is 475 grains... My heaviest is 600 grains... I want to make sure I do a ethical kill...With the kinds of bows I shoot, I think it is very important to know what Cut on Contact, KE and MO is used for.

Dwayne


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## AllenRead (Jan 12, 2004)

johnhames said:


> KE really has no relation to penetration for hunting or anything else as per Dr Ed Ashby's resurch and paper, link found below:
> 
> 
> http://www.bowhunters.org.au/bulletin.htm
> ...



I think that you have misread Dr Ashbey's paper. He says that KE has no DIRECT bearing on penetration.

This statement is a fine point of engineering semantics. As such I agree with him. The force that we commonly call Kinetic Energy he is calling Momentum.

The formula we use for Kinetic Energy is an easy and useful formula and provides us with information that can be used to compare equipment.

I hope that everyone realizes that Kinetic Energy and / or Momentum is not the only factor that influences penetration. Dr Ashbey points out several other factors including shaft size and finish, broadhead design and whether the arrow hits bone or not.

Thanks for the link to his paper. A lot of good information if you can keep your eyes from glazing over. :smile:


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## johnhames (Apr 9, 2003)

AllenRead said:


> I think that you have misread Dr Ashbey's paper. He says that KE has no DIRECT bearing on penetration.
> 
> This statement is a fine point of engineering semantics. As such I agree with him. The force that we commonly call Kinetic Energy he is calling Momentum.
> 
> ...





> KE really has no relation to penetration for hunting or anything else


Let me re-write this: KE has no relation to penetration for hunting or penetration for any other purpose. I didn't mean to imply KE 
was a usless concept.

Page 11 paragraphs 1 and 2 make it very clear he is not calling KE momentum. If fact, the way I read his paper its main focus is to point out that KE as a predictor of penetration is inappropriate and that momentum more closely predicts the penetration of a given arrow. And that further consideration needs to be given after momentum is caluclated to such forces as friction, broadhead alignment, broadhead design etc.


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