1.5). Shot placement
2). As perfectly tuned arrow/bow combination as possible.
3). Wind in your face, sun at your back.
10). Momentum
99). KE
1.5; No matter how good a shot you are, and how careful you are, you can NEVER be sure of a hit on game in actual hunting conditions.
3; You can either do your best with the circumstances or stay home. How are you ever going to get back to your truck if you hunt into a west wind all day? ;-)
I've owned probably close to 20 bows over the years and experimented with dozens of shaft/tip combinations. I've always used KE as a reference between the different setups, but I've also used a large dose of common sense to go with it. I've always shot a reasonably weighted arrow at a reasonable speed, tuned to my bow, and tipped with sharp BH's. It's served me well.
When it comes to light/fast vs heavy slow, my thoughts are exactly the same as greg simon...the answer lies somewhere in the middle.
For a given bow and arrow combination in my possession, I've got three basic tools for increasing penetration. Those are 1) draw weight, 2) tuning, 3) broadhead design.
I'm not going to go out and buy another bow or a different arrow based on a KE calculation showing my set up is generating only 67.88 ft-lbs instead of 69.43. So I don't really care what the KE or momentum number is. I'll shoot as much draw weight as I'm comfortable with, using a proper spined shaft of decent weight, and properly tune the bow. Then I'm all set to easily kill any NA game animal with a full pass through shot.
If I was planning an elephant or cape buffalo hunt, I might concern myself with comparative energy numbers for a possible heavyweight set-up. But most of us will probably never have such a need.
Because KE and momentum share the same components, momentum will increase as arrow mass increases and is therefore mistakenly given the credit for increased penetration. However, it has nothing to do with penetration. Energy is what propels the arrow and energy is what stops the arrow. KE (at the target, not the bow) and the average resisting force are what determine penetration.
Penetration = KE/average resisting force
If momentum was truly a factor in penetration, it wouldn't matter whether the momentum came from velocity or mass. Look at these two combinations of weight and velocity that produce equal amounts of momentum :
740 gr arrow @ 174fps (49.7 ft-lb KE)
350 gr arrow @ 368 fps (104.7 ft-lb KE)
Do you really think that an arrow with about 50 foot-pounds of KE will have the same penetration as one with about 105 foot-pounds of KE ? So how good of a predictor of penetration can momentum be? Try it.
These videos illustrate the point.
http://www.youtube.com/watch?v=t4RGcyZ_gJY&feature=youtube_gdata_player
http://www.youtube.com/watch?v=VAfK0sBsZBw&feature=youtube_gdata_player
Momentum relates force to time. Kinetic energy relates force to distance. Consider two objects experiencing the same stopping force. An object with twice the momentum requires twice the time to come to a stop. An object with twice the kinetic energy requires twice the distance to come to a stop. A faster but lighter object will slow at a greater rate (larger acceleration), but will have more velocity to ?get rid of?. This results in the same time to stop. Because the lighter object is initially moving faster, it travels further in the first moments. This results in a greater stopping distance. If you want the arrows to take the same amount of time to stop, balance the momentum (mv). If you want the same distance, balance the kinetic energy ( (1/2)mv^2 ).
Dr. Ken Mellendorf Physics Instructor Illinois Central College
Momentum is used for other calculations, but never to determine distance.
A catcher can stop a baseball very easily traveling at 95 mph, but the same catcher cannot stop a bowling ball traveling at 20 mph. Neither ball penetrates the catcher, but the catcher will definitely feel the effect of the bowling ball, and at a farther distance from where he started...
Yet the penetration of both were nearly equal.
Please post some real world video that shows momentum being a better predictor of penetration than KE. (only variables being weight and speed, as in the video)
KE is the perfect predictor of penetration IF the exact KE at contact and the exact average resisting force are known.
http://www.qdma.com/articles/momentum-beats-speed-for-lethal-arrow-hits http://www.tuffhead.com/ashby_pdfs/ashby%20ours/PDF%20Momentum,%20Kinetic%20Energy%20and%20Arrow%20Penetration.pdf
Or send them to me, yeah they don't work, lmao! I'd chuck my fixed heads before my mech's!
Don't get too caught up on KE, just shoot a properly spined fmj and your good to go
KE is PART of the answer, but not all of it. There are a lot of factors, weight of arrow, composition of the arrow shaft, how much weight forward of center, they type and sharpness of the broadhead, and most important of all, WHERE YOU PUT IT!
TBB
As you well know bullet kill through shock, arrow kill through blood lose. By the way, a .22 only has about 135 ft-lbs of KE.
"In the trad world it is believed that you get more energy out of the bow with heavier arrows and it quiets the bow down. Does this hold true for modern compounds? If the penetration difference in light/fast vs heavy/slow is negligible, and the bow shoots both well, it would only make since that light/fast would be the way to go due to flatter trajectory."
The amount of additional KE will vary with each bow, both trad and compound. Best to test your setup to see if the penetration difference is worth the tradeoff in trajectory and sound.
You can test this by shooting a target which is ridged and compare the penetration to that of one which is hanging and free to move and rotate.
You want the arrow to retain as much energy as possible carried forward by the moving mass of the arrow, or momentum of the arrow. Both are descriptions of the dynamics of the conservation of energy, one does not trump the other, nor ever has. They act in unison to give the end result.
I compared apples to raisins on purpose, two projectiles of different mass at different speeds to illustrate the point of light/fast vs heavy/slow - that is the premise of the discussion. Now, apples to apples would have been a baseball and a baseball at different speeds.
So, just where does the equation for KE come from anyhow and does the KE at the bow even mean anything? What KE is truly delivered downrange at the target?
redwing's Link
Very interesting for sure.
My best, paul
"Momentum is, therefore, known as a linear function, and is a measurement of the force of forward movement of an object."
If it were a measurement of FORCE, the units of momentum would be in units of force, like pounds, ounces, grams, grains, etc.
To my knowledge (I may be wrong), Ashby never documented the shaft diameter, broadheads, FOC, spine, of the arrows used his animal test. Nor did he document that the bows remained tuned as arrow weight changed. Nor we're any of the tests filmed. The tests are not repeatable or double blind and therefore not scientific.
Ask yourself why are his conclusions not demonstrated in the video that I provided above. In fact, the opposite of his conclusion appears to be true. Search the Internet or text books for ANY example where momentum is used in the calculation of distance (penetration).
Perhaps you should ask yourself why your conclusions are not demonstrated (and are generally contradicted) on game in the field. Those who have lots of experience with hunting dangerous game with archery gear pretty much disagree with your version of science - which tells me that there are aspects of it that you do not understand and cannot account for.
Still waiting for your "real world" video that shows momentum being a better predictor of penetration than KE. (only variables being weight and speed). All you ever give is opinion.
There's one fact that can't be argued.
That is what is so fickle about academia. There is the constant argument of whose explanation is correct and whose is incorrect and as long as there are two sides to the argument, what is really happening?
In this ongoing debate (past, present, and future), ALL aspects need to be incorporated to fully describe the complete phenomena of what is truly happening. It is completely absurd to say only one component has everything to do with it.
How many times does a design have to go back to the drawing board because something weird and unpredictable happened? Lots.
Like it or not, BOTH momentum AND kinetic energy have EVERYTHING to do with it AND an arrow hitting a target has the dynamics of a moving object colliding with a stationary target. A moving target is no more than the collision of two moving objects - just like two cars moving through an intersection.
KE equation means very little....potential energy in a bow maybe. For an equation to explain things it has to work in all scenarios....the KE equation falls down at both extremes of the spectrum [very heavy arrow and very light]
I would agree with Xbows comment....but when it comes to heavy game I've seen very heavy arrows and avg arrows shot from the exact same bow into water buff....and the avg arrows fail every time. Arrow weight becomes a key factor in penetration on very large animals.
Just more opinion. Where is the proof? Explain why the video does not support the momentum theory.
kadbow, what difference does it make how may elk I have shot or what my setup was? Newton never shot an elk with a bow so I guess he has no credibility with you. Make a comment about the physics or can you?
Not sure if its what matters to kadbow, but for some, its relevant to the point that the original poster asked about.
"In regards to penetration, does it matter which way you go? i.e. Light/fast or heavy/slow?"
Pretty sure he is referring to penetration on an animal under hunting conditions, and since its posted in the elk forum one could assume that he is referring to elk.
Newton may have credibility when it comes to the laws of physics but there are many here who are far more qualified to answer the o.p.'s question in regards to penetration on elk in hunting situations.
Not opinion, fact - get over it. The proof is in any physics textbook and a video will show everything but will only highlight what you want it to.
Purdue. You give this example: - 740 gr arrow @ 174fps (49.7 ft-lb KE) - 350 gr arrow @ 368 fps (104.7 ft-lb KE)
But I wonder about the bow part of the equation. If the 740 gr ad 350 gr arrows were shot from the same bow, what speed, KE, and momentum would they have (Assume the bow is tuned separately for each arrow)
I had heard that bows transfer energy more efficiently to heavier arrows.
A heavier arrow will no doubt absorb more of the KE than a light arrow and it will transfer more of that energy into momentum at greater distances.
The apples to apples would be having someone with a sling shot haul a golf ball, then same sling shot haul a ping pong ball. Lets do this several times at several distances. Oh and lets have the receiving end be you standing in place with your hands tied behind your back. Which would you rather be hit with? The slower golf ball or the extremely faster ping pong ball? Keep in mind, same sling shot same KE or stored energy.
In this case things changed too, golf ball is harder and a little bigger in diameter but what didn't change was the slingshot KE/stored energy. Bottom line, what made a bigger punch at all distances?
Seems rather simple to me. Common sense tells me I dont need to do these experiments to know a golf ball would hurt a whole lot more than a ping pong ball at any distance.
Arrow dia. tip wt. tip dia. area tot. wt. vel. mo. KE penetration % more wt. % more mo. % more KE % more penetration
Maxima 250 0.289 250.9 0.343 0.0924 498.0 199.6 0.4415 44.0663 12.000 43.64% 22.84% 5.05% -2.38%
Maxima 250 0.289 99.2 0.312 0.0764 346.7 233.4 0.3595 41.9480 12.292
Not a perfect or even a scientific test. Note the slight difference in tip diameter and therefore tip frontal area. Ideally they should have been identical. However, it was typical of other tests I have ran and somewhat echoes the results in the video. So is momentum (mo) or KE a better predictor of penetration? There is really not a dime's worth of difference between the two arrows. Is the flatter trajectory worth the noise? It's mostly about hitting a non-startled animal in the right spot.
Basically it said that 43.64% more weight yielded 22.84% more momentum and 5.05% more KE over the lighter arrow, but lost -2.38% of penetration.
Common sense told everyone that heavy objects fall faster than light ones until Galileo actually tested the theory. Try your experiment, but not to see which one hurts the most. Check for penetration. I think that's a little closer to the subject at hand.
I on the other hand, really do not have an answer. What puzzles me most is, I generally trust science theories and formulas to the fullest extent. But with that said, it would make sense that an arrow with 80 pounds of KE would out-perform or rather penetrate an arrow with 50 pounds of KE, no matter the arrow weight of either. However, say you put a dull four blade broadhead with a one and a half inch cutting circumference on the arrow with 80 pounds of KE, and a razor sharp two blade head with an inch diameter on the arrow with 50 pounds of KE, though I haven't tested this, my theory, or thoughts are, that the latter would penetrate better than the former. So undoubtedly there is more to penetration than simple numbers.
I have read numerous good ideas here that make sense, but in the end, I do believe that achieving penetration is more like a complete recipe, rather than simply a portion of the ingredients.
Another example might be something like, say you could throw a baseball to the velocity required to generate even 200 foot pounds of KE, and you throw this baseball at a deer, versus a properly set up arrow generating only 30 pounds of energy. I bet a dollar to a donut that the arrow would penetrate enough to kill the deer - again with the variables, but assuming that it is within a reasonable distance - whereas the baseball hurled at that level of energy may knock the deer from it's feet, or maybe even break a rib or something, but it certainly wouldn't kill the deer, assuming you don't hit it in the head, and even then I am uncertain that it would kill a deer. My point with this and my first illustration is that there is undoubtedly more to penetration of hunting arrows than mere numbers, though I fully believe that these numbers can be used as tools to determine penetration potential.
In the end, and to more directly address the question presented, as several have already mentioned, I believe that when speaking in terms of general big game, without adding in the debacle of dangerous game, or big bears, with all else being equal, a medium weight arrow is best. Going in the middle get's more velocity than the heavier arrows and more momentum - as it has been described here - than lighter arrows. However, as has also been mentioned, the chosen broadhead is a very important key to your quest for penetration.
And something else to remember is, whatever choice you have, I am certain that you can find someone who has had positive as well as negative experiences. Bottomline variables abound, I simply suggest picking a set up that has been tried and proven numerous times then if you choose, you can tweak and perfect it from there.
Good luck, and to all you tech savvy guys presenting all of these formulas and scientific information, please carry on, I enjoy reading it as I too, try to sort out what actually makes this or that work better, etc.
http://www.bowsite.com/BOWSITE/features/articles/equipment/penetration/
Probably the 800 grain arrow......but why? Are the arrows equal other than weight? Do they have the same FOC and spine? Hardly. 800 grain arrows frequently have one shaft inside another. This not only increases the weight, but also the spine. The opposite is true for the 350 gr arrow.
The lighter arrow will flex more upon impact, thus absorbing much of the energy. The video and my own tests show that just added weight does little to affect penetration. Do your own tests.
As I said, my test was not perfect. No test is. Ideally the additional weight should have been added uniformly so as not to change FOC or the arrow's spine. Weight tubes do a pretty good job of this.
The target was sold against my house, but it still could have jumped a little with an off center hit.
Draw length and release variations could also be a factor that a shooting machine could have helped.
These small errors in the testing procedure cause errors in the results, especially if the errors all stack up in the same direction. The test in the video was more controled than mine, but we got similar results. To me the important thing learned from the test are not the specific numbers, but the trends or direction they point to. The main one being that KE is a better predictor of penetration than momentum. I ran 2 or 3 other test with different arrows and weights and they all pointed to the same conclusion.
Please run your own tests.
The target, the arrow and the air. The more rigid the arrow the more the arrow's energy will be used to penetrate the target instead of being used to flex the arrow and move air.
Because you said you shot three elk and you don't care about momentum so I was curious what your set up was.
So again I ask what was your set up? Show me photos of the elk or can you?
No need to get defensive or offensive.
Horse power is used to measure energy as well. A 100 hp gas engine and a 100 hp diesel should be the same right? Try it and let me know what you can tow with each.
The lighter arrow does not "carry" the energy after contact as well as a heavier one. Once resistance is encountered momentum is a better indicator of how much energy is carried forward. Just as torque is a better indicator of towing power in HP, how much hard heavy work it can do..... weight in KE is a better indicator of retaining energy after initial contact. Momentum formulas lend greater value to weight than KE.
Example: 243 and a 45/70 have roughly the same KE, muzzle energy. One has taken every species of big game in NA, dangerous game as well. I wouldn't hesitate to pack it as back-up for anything, big bears, moose, anything. Hint: it's not the 243.....
In real world KE is a fairly poor indicator if used as the primary reference of terminal performance.
LOL . No, horsepower is used to measure power. Energy and power are not quite the same thing. Kind of hard to take seriously anything you say after that blunder.
"Once resistance is encountered momentum is a better indicator of how much energy is carried forward."
Now you did it again. Momentum ( which is not energy) is a better indicator of how much energy is carried forward???? Better than KE (which is energy)???? Are you serious? Are you sure you have thought this through?
The bottom line is, out of any particular bow, for maximum penetration shoot a relatively heavy arrow (8 - 9 grains per pound of draw weight), put as much of that weight forward as possible (avoid unnecessary weight at the nock like batteries). That will require a stiff shaft to tune well, which has much better terminal performance. Finally choose a quality COC head in moderate size (1 1/4" cutting diameter give or take 1/8" in about a 2-1 aspect ratio), with 2 or 3 blades in a straight, smooth configuration, shaving sharp. That is a time proven formula in real life hunting situations. Other options may work, but none work any better.
Bears charging my friend, best pick your gun.... KE.... it's all the same remember?
Kinetic Energy is the integral of momentum - the area under the momentum curve, making it a product of momentum (inertia, momentum, and kinetic energy are sequential integrals of one another). When you integrate momentum relative to a change in velocity over time, you get the equation 1/2mv^2. The total KE at the target is the change of max KE at the bow and the final KE at impact. These two values are the upper and lower limits used in the integration. The KE at the bow doesn't really mean anything. KE is really just a measurement of what the mechanical bow put into the arrow. It is the energy required or work done to get the arrow of mass to travel at a certain velocity. KE and momentum really do rely on mass as it's the independent variable and the velocity is dependent on the mass and what efficiency the mechanical bow can do work on it to propel it forward. The comparison of the two is a function of velocity.
The two say the same thing, it depends on the perspective used (you can rewrite the KE equation in terms of momentum, by the way). Momentum, as pointed out earlier, is a matter of application over time and KE is an application over distance. They can both be used to describe penetration, but neither is really the ultimate answer. That is why the end result can be deduced from both arguments. One, if it takes longer to slow it down, it also must travel a certain distance as well and two, if it can travel farther, it also takes a certain amount of time to get there.
We can begin to complicate it from there with all other variables such as surface area, coefficients of friction, applied pressure at the tip (field point/broadhead), etc., etc., etc.
In the end - does it really matter? Just get what you like, make sure it is tuned properly, practice, and have fun!!
I was using definition 2 c.
ABSORB
transitive verb 1 : to take in and make part of an existent whole
It isn't opinion, it is anecdotal evidence reflecting data points of actual hits on game animals. Call it correlation if you will - but not an opinion.
You on the other hand quote formulas from a physics book and extrapolate out results from this that are contrary to what happens in practice on game. My assessment is that you are factually correct in terms of the equations you parrot, but don't have enough of an understanding of the variables that exist in hunting situations to provide sound advice - and have a total lack of understanding as to how these real world factors affect penetration. Moreover, you are so married to your narrow thinking that you will ignore mountains of anecdotal data in order to keep faith in your intellect.
There a very good reason that folks with experience outside their living room dictate heavy arrows for dangerous game.
Still waiting on your real world video.
Again, KE is KE, I get that.... right up until it hits something. Then you can throw those equal numbers out the window. The 243 gets it's KE figures mostly through velocity, the 45/70 through bullet weight. And vastly different results on impact with large and sometimes dangerous animals. That is the point you are refusing to consider. Other variables are very different as well including trajectory. All are give and take. But neither is the same regardless of having equal KE.
And that was the OP question. "In regards to penetration, does it matter which way you go? i.e. Light/fast or heavy/slow? Is all KE the same when it comes to penetration?"
Answer: No. It is not all the same, all other factors being equal, same head, same hit, etc. It is all a trade off either way you go. See example above. Most here have given sound advice and go with a moderately heavy(er) arrow without greatly effecting trajectory at moderate ranges. You figure out what is moderate to you.
Everything in moderation is a cliche, but a good cliche.... key word for me being "everything"..... heheheheh.....
Sorry, try again?
ob·sti·nate
adjective
stubbornly refusing to change one's opinion or chosen course of action, despite attempts to persuade one to do so.
I agree, not all KE is the same because it only describes what is being done in the situation it is being applied to. A heavy mass will continue in its trajectory because it retains its energy more efficiently. A lighter mass will not continue in its trajectory because it gives up its energy more efficiently. This is when a collision occurs, as in a heavier arrow hitting a target vs a lighter arrow hitting a target.
An equal of you advice about penetration on game I suppose.
The hilarious thing about you asking for a video is you have already dismissed the most significant body of work on determining predictive variables for penetration on game animals, simply because it is not scientifically repeatable. You are so married to your sophomoric understanding of physics that you won't even try to understand the reasons that your repeatable tests come up with results that negatively correlate with penetration on live animals. Before you go down the predictable path, I don't take Ashby's work as gospel. But there is an overwhelming and undeniable body of evidence (including his study) that contradicts what you think you understand based on test media that is not an animal.
You finally found it, but don't know what you have.
Right out of a first year physics book:
Distance = KE / resisting force
Distance = (1/2 m V ^2) / resisting force
Distance = (1/2 m V V) / resisting force
Distance = (1/2 momentum V) / resisting force
From the above formulas you can see that if mass increases it doesn't matter which formula you use, the resulting distance (penetration) will be the same. Mass that increases KE also increase momentum. Also, increases in mass means decreases in velocity for each formula. Any chance has the same affect on penetration. I hope that makes sense.
Also, this demonstrates why KE is a better predictor of penetration. In the top formula there are only 2 variables. Since we are assuming the resisting forces are equal there is really only one variable that determines penetration......KE.
In the bottom formula there are 3 variables or really only 2 since the resisting forces are equal. You must know both the momentum AND the velocity to predict penetration. Using only momentum would be very misleading, as my data demonstrated.
I know this is just a foam target but is 1.5" of extra penetration worth bigger pin gaps? Yeah, I'm probably just being picky and over analyzing this but I'd still like to hear some opinions.
I'm shooting a Hoyt Spyder @ 65lbs w/26.5" FMJ 400's
My 2 cents is that it comes down to your range estimation ability and the difference in penetration and accuracy at 80 yards. Test all these. Think twice before taking an 80 yard shot. Wind and animal movement can screw things up.
Try doing some "stump shooting" at unknown ranges and wind conditions to check your range estimation and accuracy in various terrains.
Actually I do, and had it all along. Remember, I did ask earlier on where the equation for KE came from? Mass is everything and what makes it all work. Velocity, elapsed time, distance moved is dependent on mass and how that mass spends its energy.
The heavier the projectile (arrow) the slower it will move in a set system such as a bow imparting what energy it can into an arrow, just a fact. This is why in 1278 A.D. an invading army would use catapults flinging 1 ton rocks at city walls to break them down as opposed to 1,000 men flinging arrows at the wall from 50 ft away (assuming they wouldn't be killed in the process).
Because mass is a constant it means that KE comes second to momentum (which is an object of mass in motion). You can't have energy in motion until you have mass in motion. Calculus shows this in the integration of momentum and the only changing variable with respect to time is velocity. They can both be an indicator of penetration - just depends on the argument you choose to present, but don't dispel one over the other because you don't agree with it. They do both have to be present and they both need to be present to tell the whole story. The entire discussion has shown that because something has a higher KE, doesn't necessarily mean it is better and just because something is way heavy doesn't mean that it is the best either. I think someone said earlier to find the happy medium for your setup and go from there. That is a very correct statement.
Really? Make it work without velocity. Both are needed.
"Because mass is a constant it means that KE comes second to momentum (which is an object of mass in motion)."
KE by definition is also mass in motion. Second in what way?
"They can both be an indicator of penetration ......"
That's true. KE is a good predictor and momentum is a poor one. Look at the video and my test data again. Explain why the arrows with significantly more momentum did NOT have significantly better penetration.
If you only know the KE and the average resisting force, penetration can be determined exactly. It doesn't matter if most of the energy came from mass or velocity.
If you only know the momentum and the average resisting force, penetration can NOT be determined. The mass or the velocity most also be known. The formula clearly shows that.
Therefore KE is the better predictor of penetration.
Momentum in terms of KE -
p = mv, and KE = 1/2mv^2
If KE = distance, let d=distance, then KE = d
If d = 1/2mv^2, then v = (2d/m)^1/2
If p = mv, then p = m((2d/m)^1/2), and p^2 = m^2 (2d)/m
Then d = p^2/2m
So, penetration in terms of momentum. Carrying it further, you do eventually end up with 1/2mv^2 - but you get there terms of momentum.
The two are related, KE is a function of momentum. Velocity is the function of the work done by the bow on the arrow with mass. You can't have either momentum or kinetic energy without mass or velocity, but the velocity is still the dependent variable. The object in motion imparts a force on the target, KE does not. Momentum is a vector quantity, KE is a scaler quantity.
KE used in the archery world today is really a marketing tool to sell a product.
I had 3 arrow setups tuned FOR THE SAME EXACT BOW- an 80# Allegiance. 440gr, 560gr and 840gr
We shot multiple shots into water buff with the 2 lighter arrow setups [the 840 got complete pass thru and was what killed the bull] bottom line;
The penetration from multiple shots with the light arrows was anemic- not even close to the very heavy arrows. now of course you cannot say this is a perfect comparison as every shot is different on an actual animal.
KE equation FAILS MISERABLY....efficient BH's and arrow weight do more to tell the story OF PENETRATION, IMO.
Where do you come up with this stuff? KE doesn't equal distance, it's energy.
You still haven't explained why momentum didn't do a better job of predicting the penetration in the video and in my data. KE beat it, hands down. Seems like marketing is on the right track to me.
Thanks for the pictures. Did all three arrows have the same spine? Did all have the same broadhead? Did all hit the ribs squarely and oriented in the same manner? Did all go through the same thickness of rib?
It's just impossible to do a conclusive test on an animal.
"KE equation FAILS MISERABLY.."
Newton came up with it, not me. If you can prove it's wrong, you have a trip to Stockholm in your future. And exactly how did it fail? Surely the heavier arrow had the greater KE and it also had the greatest penetration. How is that a failure of the KE equation?
The penetration formula shows us that maximizing KE and minimizing the resisting force will yeild the greatest penetration. Things like bow poundage, draw length, arrow weight, and cam design can increase KE. Things like broadhead design, number of blades, blade sharpness, point rigidity, frontal area, bow tune, arrow spine and maybe FOC can reduce that resisting force.
With all this said, hitting the right spot is number one.
Good job on that buff.
Where do I come up with this from? From your own post. You can factor out the resisting force because it is constant with both KE and/or momentum. The resisting force is drag, the target, etc.
The real indicator of penetration is the extremly high pressure applied by the force over a very small area as exhibited from the broadhead. The force comes from the object of mass relative to change in velocity over time (or accelaration), not energy.
Is there such a thing as someone sinking in quicksand and argueing they aren't?
What you do to one side of the equation you must do to the other. You can't just make unequals magically equal.
"The real indicator of penetration is the extremly high pressure applied by the force over a very small area as exhibited from the broadhead."
Actually it's just the opposite. The arrow which see the least pressure will have the greatest penetration. Your thinking is backwards.
Still waiting on your explanation as to why momentum didn't do a better job of predicting the penetration in the video and in my data.
but build a 500 grain arrow, sharp cut on contact broad and shoot it out of a bow made later than 2000 and you will kill any North American big game animal - probably with a hole on both sides......
Regardless, your post is direct and hilarious.
First, lets agree that we are talking about reasonable modern archery set-ups, not some theoretical extremes.
Second, you must accept that a heavier arrow will out penetrate a lighter arrow from the same bow with everything else being equal. This is consistent with all the testing done on animals, and years of real world experience. When going after BIG game, everyone shoots a very heavy arrow. While that may mean more FOC and a stiffer shaft, those are secondary advantages to the increased weight.
Take a 500 gr arrow at 250 fps and solve for KE. KE = 69.41
Now substitute a 400 gr arrow and solve for velocity at the same KE V = 279.5.
Now solve for momentum in each case. 500 gr = .555, 400 gr. = .497
The heavier, better penetrating arrow has a higher momentum at the same KE as the 400 gr. Now in the real world, the results are even more dramatic because as we all know, in most cases the heavier arrow will actually have a higher KE and momentum out of the same bow, likely more FOC and probably a stiffer shaft, all of which will improve penetration.
You are trying to make the KE Equation explain "Everything" penetration in an animal....its a misapplication of the formula, all of the dangerous game guides and experts know this as fact.
Hey, in most thin skinned NA game this is a mute issue due to the incredible efficiency of a bow shot arrow- there is little distinction.
You have a handle on two of the really big factors. Bow tune and animal movement are two more.
Ziek, if I understand you, you started off with your fore drawn conclusion, then accept facts not in evidence, then ignore inequalities in the testing, then calculate numbers to suit your purpose. That is not how things are proven logically. It does not explain the video or my data.
beendare, The laws of physics apply all the time, not just when hunting. Newtonian physics is applicable all over the universe except when approaching the speed of light or splitting atoms.
Distance = KE / average resisting force
You can use this formula to calculate how far a car will skid or how far you can spit a pumkin seed. The hard part is usually determining the avarage resisting force.
Heavy arrows work. They can work better than light arrows when all else equal. They usually have more KE and retain that energy better than a lighter arrow. I agree. However, their advantage is slight at close range, as the video and my data have shown. I suspect there real advantage is that the weight come in the form of thicker shaft wall (more spine) and perhaps heavier broadheads that increase FOC. But the arrow weight always gets the credit from the momentum crowd.
When an actual controled test is done, where only the weight is altered, the truth comes out; weight has only a slight advantage at normal hunting range.
Now maybe an elephant bow with 800 grain arrows pick up a far greater percentage of KE, I don't know. But tests show that typical weight bows and arrows just don't see much advantage. You can ignore your own eyes if you want.
X-man, I knew you would have something important to say.
If you want to appreciably change KE you must do so at the bow - change draw weight, draw length, design, or efficiency.
Ziek, "But certainly not enough to account for the increased penetration that every experienced hunter has noted, and is generally accepted as fact."
The "every experienced hunter has noted" is just not true. Why have bow manufacturers hyped the speed of their bows for years? Because it sells bows. Why would they waiste money developing and marketing faster and faster bows if they didn't sell. Now why would people continue to buy faster and faster bows if they did't work? So there must be a lot of satasfied hunters out there that use fast, light arrows for hunting.
Also, how many hunters actually experiment with different arrow weights. Most start off with a setup similar to a buddy's, either light or heavy. If it works, which both will, they stick with it. Many on this site, as well as the guy in the video, have never had a problem with a light setup.
"Momentum changes more significantly as you increase arrow weight."
Why do you say "more significantly"? Momentum is changed equally by changes in either mass or velocity.
I should have said; every experienced bowhunter who has shot both heavy and light arrows. But even so, those same light arrow proponents would certainly opt for heavy shafts if they were to hunt elephant. Why? Because presumably they would rather kill the elephant than get trampled by it and heavier arrows penetrate significantly better. That's a fact!
"Why have bow manufacturers hyped the speed of their bows for years? Because it sells bows. Why would they waiste money developing and marketing faster..."
Two reasons. Because faster bows also launch heavier arrows faster, increasing momentum and flattening trajectory. And, most bowhunters shoot primarily tender little whitetails that are not particularly hard to penetrate. So they put more value in flat trajectory than penetration potential.
"Most start off with a setup similar to a buddy's, either light or heavy."
True. And most just buy whatever manufacturers hype without much additional thought.
"Momentum is changed equally by changes in either mass or velocity."
But KE changes by the square of velocity.
We are not talking about what is ADEQUATE penetration. The original inquiry was what produced INCREASED penetration out of a particular bow; light and fast or heavier and thus slower. And what is a better predictor; KE or momentum. I can't believe there is still any debate about that.
KE is worthless to archery hunters for the most part. KE in the sense that it impact arrows/bows is simply the energy required to get the arrow from 0 to top speed.
that's it - nothing more, nothing less
it doesn't have any impact on energy transfer when the arrow hits, penetration etc
But when they added significantly more weight they usually have change the arrow's spine and FOC too. We don't really know the affect of just the weight.
"But KE changes by the square of velocity."
True, and I was not questioning that part of your post, was I. Explain the "Momentum changes MORE SIGNIFICANTLY as you increase arrow weight."
"The original inquiry was what produced INCREASED penetration out of a particular bow; light and fast or heavier and thus slower."
From the actual evidence that has been presented:
1) Heavy arrows have a very slight to insignificant advantage at close range, but their advantage increases with range, at the price of trajectory.
2) From uncontroled tests where other variables are changed in addition to added weight, extremely heavy arrows shot from extremely strong bows show a distinct advantage in penetration. It is unknown what percentage of the additional penetration came from the added weight or the other changed variables.
3) In controled tests where only the weight is changed, it appears that KE is a significantly better predictor of penetration than momentum. Newton's formulas also verify this.
Please run your own tests and post the results. Prove Newton wrong.
Now that's just silly. Where does the energy go? Energy is transferred all the time. Why do you think a car's brakes get hot. KE was transferred into heat energy.
Potential energy starts the arrow moving, the moving arrow has KE because it has mass and velocity. A variety of resisting forces like friction, frontal drag, shear force, etc. act upon the arrow in the opposite direction as it moves through the target. As the arrow slows its KE (and momentum) drop. Since energy can not be created or destroyed the energy was transferred to move material, generate heat and generate sound. All of these are forms of energy. It take energy transfer to stop the arrow. Just like in a car.
So you agree, heavy arrows penetrate better. The only question is by how much?
And in the real world does it matter whether the increased penetration comes just from the added weight, or a combination of the added weight and the increased spine and FOC that usually accompany it?
KE is a valid comparison between bows shooting the same arrow. But the bow does't penetrate anything, the arrow does. Mass effects penetration more than velocity, so the equation that gives more relative value to mass and less to velocity is a better predictor of penetration potential.
I'll try one more example with our elephant hunters. Both shoot a 100# bow at the same draw length. One is equipped with an arrow at a weight that leaves the bow at 320 fps. The other shoots a 1000 gr arrow at whatever velocity is produced. Is there any doubt who has the better set-up to achieve adequate penetration.
If you feel the earth shake a bit its not an earthquake. Its just the physicists that worked out the basics long ago rolling over in their graves.
GRoe's Link
As to the question of light/fast vs heavy/slow. I would error on heavy over light anyday of the week and twice on Sundays.
GR Heads Up Decoy
Disagree.......just go after those species above with Wh gear ?
Good concept for a Book " Use Enough Bow"
As bb has varified, that has been my position all along.
"And in the real world does it matter whether the increased penetration comes just from the added weight, or a combination of the added weight and the increased spine and FOC that usually accompany it?"
Not to me. If it works, it works. It just bothers me when everyone claims it is due to the weight without acknowledging the other variables that they changed which also affect penetration or saying momentum trumps KE for predicting penetration when it clearly does not. Everyone just keeps saying what they have always said without running their own test or even believing their own eyes.
"Mass effects penetration more than velocity...."
Except when you actually test it. Have you forgotten the video and my data.
As for your elephant example, the heavier arrow should get more penetration because it received more KE from the bow and is usually a MUCH stiffer spine. Haven't I been over this before?
Most seem to think that momentum and weight are almost synonyms.
The momentum of an object is the product of its mass times its velocity. Momentum is NOT a type of energy but it can be related to kinetic energy mathematically. There is a difference in terminology between the words speed and velocity. Speed is just a number, velocity is speed with a direction. For KE, either can be used and the resulting number, the energy, has no direction. Velocity is used in the momentum calculation because momentum is a vector quantity; or rather momentum is a measure of the speed of the object along with its direction, times its mass.
Arrow #1 Dynamic Spine is .250, Arrow weight is 798.6, FOC is 11.9 %, KE is 98.59 shot out of a Hoyt Nitrum Turbo at 70 lbs and 30" draw
Arrow #2 Dynamic Spine is .250, Arrow weight is 425.6, FOC is 11.92 %, KE is 103.29 shot out of a PSE Omen at 70 lbs and 30" draw
Which one is going to penetrate better? Which one are you going to take on a Cape buffalo hunt?
Oh and the momentum numbers are Arrow #1 is .835 and Arrow #2 is .62 Arrow #1 is slightly larger in OD as well.
I can tell you in my photos above where the 840gr arrow killed the bull ...and the lighter arrow failed- both were .300 deflection though the failed arrow was in effect stiffer due to less point weight. Both had 2 blade heads....
No, but most here realize the standard KE formula puts a higher value on fps whereas the the momentum formula is skewed more to mass. Momentum isn't perfect but much more related to terminal performance than KE. All else being equal, COC head, number of blades, blade angles, cutting diameter, sharpness, tune, etc. etc.
Once again, the OP question.... " In regards to penetration, does it matter which way you go? i.e. Light/fast or heavy/slow? Is all KE the same when it comes to penetration?"
And once again the answer in NO.
Equal KE does not correlate to equal terminal performance all other factors being equal. As shown here many times in many cases. Nor does it correlate to equal trajectory or pretty much equal anything other than KE in a classroom laboratory.
One more test I just did. Two arrows out of the same bow:
Arrow1: 468 gr, 256 fps, 68.1 KE, .53 Mom.
Arrow 2: 546 gr, 239 fps, 69.3 KE, .58 Mom.
While both KE and Momentum show an increase with the heavier arrow, KE increased by 1.7%, while Momentum increased by 8.6%. At least at an academic level, Momentum gives a better idea of penetration potential, and it's possible, as Fulldraw demonstrated, that two different weight arrows could have virtually the same KE and significantly different Momentum.
While I enjoy a good physics debate as much as the next guy, I will share some ACTUAL observations from tests that I did when I was preparing for my 2014 elephant bowhunt....rather than rehash some elementary equations. There was a very real chance that if things went south, this hunt could have resulted in someone being seriously injured, maimed, or killed...so it was worthy of our best efforts....in fact, another very respected PH in Africa was just killed last week.
In my preparations for the Mozambique bowhunt, I initilly changed only ONE variable at a time.....but I tested several variables. I used Delta nine pound foam for my target, as it easily stops arrows from bows with up to 112# of draw weight. Understand that I am completely aware that nine pound may not perfect replicate animal tissue.....but from my point of view, it will indicate which set-up provided the most penetration RELATIVE TO THE OTHER SET-UPS.
In a nutshell, there is a point of diminished returns for everything. Like Wyobullshooter stated, the answer lies somewhere in the middle.
I varied arrows (keeping all other variables the same) and shot (recorded) penetrations. I varied poundages and kept everything the same. I changed bows, broadheads, etc. Eventually, I started to conduct tests requiring two variables being changed per experiment.
While I believe that I did a reasonable amount of research and experimentation, for the record, it needs to be stated that I did not "re-tune" the bow, everytime that I changed every variable. For all of the possible combinations, it would have been time prohibitive....and in the cases with extremely heavy broadheads, optimum flight was impossible to achieve.....good flight was possible....optimum flight was not.
What I personally OBSERVED, was the following.....
A reduced arrow diameter, a very well tuned bow, and super sharp broadheads consistently ranked high in my variables of note. Reducing arrow diameter was of high importance because an elephant rib has the potential to stop most arrows from penetrating completely....that will not be a factor for North American game.
I also noted that the technology offered by newer bows really provided more penetration than my 15 year Mathews Custom Safari "dinosaur" maxed out well over 100#. The newer technology of the MR5 at 83# seemed to be one of the better platforms....but I chose the stay with my 92# Elite GT500 (not as old as my "dinosaur", not as new as the MR5)...after all, I owned the GT500....I would have had to buy an MR5...and at some point, cost becomes an issue if the results to be gained are a modest improvement or less.
I experimented with poundages ranging from about 80# to 112#. Arrow weights (and the varying spines that come with them) from about 510 - 1300 gns. I considered VPA, Ashby, and German Kinetic two bladed broadheads. What I personally OBSERVED, was the following.....
I got optimum penetration from an extremely well balanced 92# bow, that shot an 820-ish grain arrow, with either a 180 grain or 210 German Kinetic broadhead. Their results were impressively similar. A hooter shooter was used....so if people want to argue about removing the "human element", so be it....but I was looking for outcomes RELATIVE to other set-ups. My arrow flight was excellent.
In my personal summary, by reducing my arrow diameter (and to some extent, arrow spine and arrow weight), I was able to find a combination of variables that out penetrated others....while still allowing practically "perfect" arrow flight. I would have preferred heavier shafts....but we simply couldn't get them to fly as well. Those massive 300+ grain broadheads are impressive, but they seemed to compromise optimum arrow flight....by using a somewhat lighter tip, I could use smaller diameter shafts which gave me better flight, resulting in better penetration through a homogenous medium.
Additionally, I conversed with a world renowned archer that has bowkilled several elephants....he has used high poundage bows, and heavy arrows previously....but his most effective set-up to date was with an 80 pound bow, super sharp broadheads, and 790-800 grain arrow weights....remarkably similar to my findings.
I am not in the faster/lighter camp....I am not in the heavier camp either.....I experimented for months with all of the variables which I felt needed to be considered, and made my own decisions accordingly.
Surfnturf....I suggest that you do the same....draw heavily from much of the sage advice offered on this thread.....but ultimately, find a set-up that works for you, and use it. Your advantage is that your prey does not require you to consider spines, weights, and poundages that may compromise optimum arrow flight....the best of all worlds is within your grasp....experiment accordingly....Good luck.
12yards, I wouldn't hunt elephants with my setup either! That said, I don't hunt elephants. If I did, shooting a very heavy arrow wouldn't be an issue, since the shot distance would be so close trajectory wouldn't be an issue. I've found that for what I hunt, 6-7gr per pound of draw weight is a good compromise between weight/speed. That said, I have a short D/L, so I don't have the luxury those with a longer D/L enjoy. In order to maximize my penetration potential, I shoot a small diameter shaft, COC BH's, and I'm pretty anal about making sure I have optimum arrow flight. The trick is finding what works best for you, taking into consideration the animals you hunt, as well as your effective distance you shoot at those animals.
Does being a custodian at a local university qualify for being an expert? :)
The heavier arrow in the video and my data had 6% and 5% more KE, yet the penetration was virtually the same. So where is the advantage to more energy being transferred to a heavier arrow? Perhaps 800 + arrows do pick up significantly more KE, I don't know. But a 6% increase doesn't seem to mean squat in a controled test where weight is the only variable that changed.
I have seen video and YZF-88 photo above that do show an advantage to a heavier arrow as range increases. It seems to be beyond 30 yards from the limited info that I've seen.
".......but I can't fathom where one with real world experience would think lighter is a better penetrator. "
No one here has said that. You are now arguing against something that has not even been put forth. What has been shown and proven mathematicly is that KE (by its self) is a better predictor of penetration than momentum (by its self). Also, that at close range, weight alone has virtually no effect on penetration.
The testimonies that favor heavy arrows are really about a heavy arrow "system" where weight, spine, FOC, etc. are all changed and the "test" is usually unrepeatable. No one knows if their success was because of less bow noise, spine, shaft diameter, etc. Yet the praise always goes to the fact that they used a heavy arrow.
Medicinemann did it the right way. He actually tested different setups and did so in a homogeneous medium. If I'm not mistaken, he found that the setup with the most KE did NOT yield the most penetration. This was due to poor flight with that setup which increases the resisting force and deminished KE at the target. ___________________________
Medicinemann, if you are still out there, how did you determine arrow flight and what were the actual KE or velocity of each setup? ___________________________
Ziek: "One more test I just did. Two arrows out of the same bow: Arrow1: 468 gr, 256 fps, 68.1 KE, .53 Mom. Arrow 2: 546 gr, 239 fps, 69.3 KE, .58 Mom."
So how did the penetration compare?
"Medicinemann did it the right way. He actually tested different setups and did so in a homogeneous medium. If I'm not mistaken, he found that the setup with the most KE did NOT yield the most penetration. This was due to poor flight with that setup which increases the resisting force and deminished KE at the target. ___________________________
Medicinemann, if you are still out there, how did you determine arrow flight and what were the actual KE or velocity of each setup? ___________________________"
Medicinemann:
My observations regarding arrow flight were subjective in nature. I would paper tune the bow/arrow combinations.....I did not keep most of those findings....once the elephant bowhunt was cancelled by the government, I was so disappointed and micturated that I pitched all of my results.
As I recall, in some cases, the set-ups with highest KE did outpenetrate those with lower KE....HOWEVER, other variables must be considered before drawing any conclusions.
For example, the really heavy arrows had a "lip" where the broadhead ferrule was smaller in diameter than the arrow shaft...which would affect penetration...whereas the smaller shafted arrows matched the broadhead ferrule diameter, and therefore presented no "lip". My heavier arrow set-ups frequently had larger diameters, and those increased cross-sectional surface areas introduced more drag when penetrating the high density foam.
Another consideration was that while I possibly shot enough arrows (where population sample size n is > or = to 30) for statistical significance, I never did a computer generated, multivariable analysis of the findings. Like I said, I observed findings, recorded them, and began eliminating certain combinations based on those findings.... without basing my results on standard deviations, etc.
I remember shooting two arrows of each set-up, and recording the penetration by simply measuring the amount of arrow sticking out of the back of the foam. Then I would switch broadheads on the arrows and shoot again. In most cases, the results were similar....but it allowed me to rule out that one arrow was flying better than the other, where superior flight explained the better penetration....even then, it was slightly subjective....if one of the arrows hit in a piece of the foam which had been sliced previously, did that reduce the resistance to a point where it permitted increased penetration? Yet more wiggle room for debate....
Smaller diameter arrows limited the poundage that could be used (due to spine) in some tests...especially with real heavy broadheads on the front of them....thus limiting the KE that I could have gleaned from them. Based on chronograph readings from right in front of the riser compared to chronograph readings from twenty yards downrange, I remember the "leakoff" being about 7 ft/sec over the first twenty yards. Heavier arrows had larger drag coefficients and didn't fly as well.
As was previously stated, my best results seemed to be somewhere in the middle....but were somewhat constrained by physical parameter limitations.
The problem is that I could have analyzed or "scienced" this thing to death....but as enjoyable as the process was, at some point in time, I had to be satisfied that my decisions to rule out certain combinations, gave me an archery platform that I was willing to take up against the largest land mammal on earth. I was comfortable with my selections. Now, if someone wants to fund a grant that will pay for the time it would take to test every variable, and really put this pig to rest, let me know....in the meanwhile, I was quite comfortable with my personal choices and decisions.
Amateur physics hacks wrongly applying a formula....in this case, KE equation and attempting to explain arrow penetration
Then we have totally irrelevant arrow "tests" that use a media stopping arrows with friction on the shaft
The originating thread was inquiring about penetration. I simply shared some findings and observations. While they may be irrelevant to you, it was my hope that they might be of interest to some others.
c3's Link
When shooting with fingers the arrow bends significantly and is not in column when striking a close target. Having an arrow perfectly in column to the direction of travel is a huge piece of the penetration puzzle.
Given two arrows of equal stiffness where one is heavier than the other, they will exhibit unequal specific stiffness. That is the stiffness relative to weight. The lighter arrows will have a higher specific stiffness and stop vibrating much more quickly than the heavier arrow. In otherwords they vibrate from the bending moment at release at a higher frequency. Carbon versus metal structures exhibit this quite clearly in many applications. Modern structural analysis often use this frequency response to determine a parts stiffness. Pretty cool stuff to say the least.
In the case of a finger shooter the heavier arrows are staying bent longer and are not 'as in column' when they hit a close target as the lighter carbon arrows. The heavier arrows are losing energy to bending further out of column as they strike the target and thus not penetrating as well.
This effect of specific stiffness was the reason many folks used to claim that carbon arrows out penetrated aluminum arrows.
I've attached a link that clearly shows the finger shooter cycle causing the arrow to be out of column even out to 20 yards or more.
Having your arrow fly perfectly in column into the target is significantly more important than whether your arrows are 350 grains or 500 grains with regards to penetration.
Back to the OP's question, I lean on the lower end of the weight scale for north American game, because I seem to have a way of screwing the pooch on range estimation even though I've used a range finder in every case. For me hunting western muleys and elk at moderate ranges when they are constantly moving makes ranging much more difficult than it might sound. Especially for one with a short draw length, oldmanitis and a hankering to f'ing up virtually every perfect stalk I seem to be able to do :)
Cheers, Pete
JTV mentioned his 370 grain arrow taking down any deer. That can be true but his shots are either limited or the arrow won't get pass thru's 100% of the time. My uncle shot a buck last year. Hard quartering away with a Mathews Z7 at 29.5" draw and 66 lbs. He got no exit hole and he didn't hit the opposite shoulder. We finally caught up to the buck 16 hours later to end things. I honestly think a mid 400 grain arrow would have helped.
I agree with Beendare on its hard to compare penetration on a target that stops arrows by friction. I think Beendares photos are a good piece of info on telling the tale about penetration. Is it perfect? No but its better then a foam target.
Last but not least I think KE plays a role but there is way more to it then KE. The two arrows that i mentioned above defiantly raise a question about KE.
Cj, thank you for reasoned response and something that should be considered. I do, however, want to point out that my test was done with a compound bow, shot with a release and it echoes the video results.
Fulldraw, "Last but not least I think KE plays a role but there is way more to it then KE."
Absolutely ! Resisting force is in the equation too. A lot of things can effect the resisting force.
Zeik, I don't agree with your reasoning about foam, but wonder what homogenous material do you thing would make a valid test medium?
Momentum is a function of kinetic energy therefore has relevance. What we have is momentum vs force, the greater the momentum the greater the force needed to impede momentum, our force here is constant for the sake of argument. So the arrow with more momentum will require more force to deviate it from its path. In this case the forces are friction of the medium used to stop the arrow, or an animal regardless of blood, guts, foam, packing nuts..whatever, it is all friction.
Purdue painted himself into a corner and tried to back pedal using numerous uncontrollable and even immeasurable variables.
I would like to see a program that you can plug and go to get your setup's energies from. Say you plug in 350gr arrow moves 300fps, then the program will then spit out what is the optimum arrow weight over the individual's max range. Of course it will have its limitations, but it would yield a nice reference.
Ohiohunter makes a good point....there are a million and a half variables that could all be debated...but until someone offers constructive criticism in the form of a better rib approximating arrow stop than my foam, I remain comfortable with my choice.
Additionally, until some of you have put an arrow through an elephant rib, don't tell me that withdrawing the arrow from the rib is any easier to retract than pulling the arrow back through foam....
Of the two arrows they have the same dynamic spine but the static spine won't be equal. To get the two bows to the same KE all one would have to do is turn down the bow for arrow #2. But that would change the static spine even more. The OD plays a role but the lighter shaft has a slighty smaller OD to aid in its penetration.
When I talked to a couple of PH's this winter they said I would be fine on a buff hunt with that arrow build for arrow #1. I know they would not like arrow #2.
It depends on the target material. Apparently this is true in foam. On animals, the most comprehensive study done was the Natal Study by Ashby, and he concluded KE was a poor predictor of penetration on actual animals, momentum was better, and arrow weight better yet (especially when bone was hit). Some folks on this site are prone to dismissing Ashby's work because it isn't controlled, but with the sheer volume of data there are generalities that I personally believe are very relevant. And again, shooting foam appears to lead folks to contrary conclusions versus what occurs on animals.
So when you say it, it's a good thing, but when I say it, it's a bad thing. LOL
"....our force here is constant for the sake of argument. So the arrow with more momentum will require more force...."
What?????
"In this case the forces are friction of the medium used to stop the arrow, or an animal regardless of blood, guts, foam, packing nuts..whatever, it is all friction."
There is friction involved, but it's just one of the resisting forces. The resisting vector force, due to the shear forces of the arrow going through bone and muscle, is not friction. Neither is the frontal drag.
Surfnturf, "As else being equal including KE, Light/fast vs Heavy/slow, penetration should be the same true?"
Yes, but it's really hard to keep all else equal.
Fulldraw, How did you measure the dynamic spine? How does changing the poundage chance the static spine? Are you sure you don't have these confused?
Since you know the KE you must have shot them in a target. How did the penetration compare?
Ziek: "One more test I just did. Two arrows out of the same bow: Arrow1: 468 gr, 256 fps, 68.1 KE, .53 Mom. Arrow 2: 546 gr, 239 fps, 69.3 KE, .58 Mom."
So how did the penetration compare?
Mad_Angler's Link
I think all the data presented so far shows that they are NOT the same. Out of a given bow, a heavier arrow will have more KE.
The link above is from Pat's penetration study before his cape buffalo hunt.
Using a 980 grain arrow gave him 11% KE versus a 655 grain arrow. That 980 grain arrow had MUCH better penetration than the 655 grain arrow.
Now, he could have amped up bow to get his 655 grain arrow to have as much KE as the 980 grain arrow. Maybe then, the 655 would have had similar penetration. But that would have required a much more powerful bow (and then the 980 grain from that suped up bow would have penetrated better than the 655).
(up to a limit as demonstrated by MedicineMan)
Good grief!!!
The "test" gave very misleading results because one broadhead failed to exit the plywood. Not even momentum predicts that much difference in penetration results. In this case the shear forces requires to cut through the plywood far exceed the friction force on the shaft. Once the broadhead breaks through the resisting force drops dramatically, allowing it to coast much further until it finally stops.
The heavier arrow with its greater KE still would have gone further, but not by as much had both broadhead either remained in the plywood or both had penetrated it. ________________________
I'm guessing Fulldraw and Ziek don't want to post the results of their test because maybe they didn't get the results they expected???
First, that wasn't what the test was about. I was simply showing that, shot from the same bow, a heavier arrow produces a greater change in momentum than the change in KE, making momentum a better (more obvious) predictor of penetration.
The arrows were very dissimilar in spine, FOC, and probably more importantly material (All carbon produces more frictional heat than FMJ, stopping them more quickly in foam).
Penetration in foam is likely not indicative of penetration in animals, and I didn't have a new piece of foam to use anyway. We all already know that out of the same bow, a heavier arrow will penetrate more.
Arrow #2 was out of a different persons bow. I just borrowed his numbers for you.
You could read Ashby's work, which reflects that the factors that predict penetration on foam (at least per the above) do not translate to animals.
No.
Equal KE does NOT equal the same performance on impact with animals. Lighter objects achieve KE from speed, slower speed objects get it by increased weight. They both archive equal KE numbers but get there different ways. But field performance on many levels is not "equal"... the actual KE energy number has limited application.
KE will ONLY tell you what the object has at IMPACT. Beyond initial contact KE loses it's relevance. Might as well try to predict trajectory with KE, after all they both have the same energy....
The heavier the object (mass) the more it will resist a change in motion. Greater mass the more resistance to that change. That change in motion can very well be an animal.
That is why the 45/70 will pound down a charging grizz in it's tracks or kill a ton on the hoof of bison.... train loads full of them actually... where the .243.... lets say it struggles under such criteria. Despite having near identical KE.
In contrast... I wouldn't want to shoot antelope or yotes at 200+ yards with the 45/70 either... not that it can't, any more than it would be possible to kill a charging grizz with a well placed .243... just that it is not the optimal tool for the job. A drastic difference of field performance despite having equal KE.
KE may have use in comparing different bows and their POTENTIAL performance. But not necessarily individual areas of performance, penetration, trajectory, etc.
Those areas of performance depend greatly on what combinations of speed and mass you should choose to GET that KE figure. NOT the KE number itself.
I wouldn't say that penetration in foam would perfectly equal penetration in animals, but I believe it likely would be correlated which is all that is necessary for comparative studies.
If you're that hell bent on it get a fresh new target collect your data, then get a fresh block of ballistic gel and collect more data then compare. Heck, you could do the test w/ 2 different new targets. Either way you need a consistent medium to shoot into.
Why do you think bullet companies use ballistic gel and not a stack of pigs? Why? b/c it is consistent and measurable, animals are not ie uncontrollable variable.
If you're that hell bent on it get a fresh new target collect your data, then get a fresh block of ballistic gel and collect more data then compare. Heck, you could do the test w/ 2 different new targets. Either way you need a consistent medium to shoot into.
Why do you think bullet companies use ballistic gel and not a stack of pigs? Why? b/c it is consistent and measurable, animals are not ie uncontrollable variable.
If you're that hell bent on it get a fresh new target collect your data, then get a fresh block of ballistic gel and collect more data then compare. Heck, you could do the test w/ 2 different new targets. Either way you need a consistent medium to shoot into.
Why do you think bullet companies use ballistic gel and not a stack of pigs? Why? b/c it is consistent and measurable, animals are not ie uncontrollable variable.
Not so much on bison....
I've passed through a lot of animals over the years with 2413 aluminum shafts that most foam targets had no problem stopping.
Animals OTOH are self lubricating.... elephant ribs not withstanding.... =D
Responses such as this are off base and untrue.
TD touched on this.
Ziek, there is foam and then there is foam. I'm not referring to high density foam as is typical of animal targets. I use a relatively low density foam in my targets. Arrow typically penetrate 15" or so from my trad. bows and more with a compound.
In pushing the arrows through by hand with this foam, it feels pretty much like pushing an arrow thru a water melon or for that matter, an actual animal.
One can wipe the arrow shaft with a lubricant to approximate the friction reduction in tissue. That said, it is debatable to claim there is very little friction on the shaft in tissue. Even on water melon which is very liquid, you can feel the friction on the shaft.
Exactly, this whole thread is arguing the laws of physics. Absolute waste of bandwith if you ask me. A whole lot of what ifs and very little empirical data. This redneck physicsology at its finest.
Agreed, your foam would be better, and a watermelon, probably better yet, but they still don't replicate living tissue very well. Your lubricant is a deplete-able resource in foam, unlike tissue (or watermelon), which continues adding lubricant. Live tissue wounds typically, reflexively contract, opening the wound, reducing shaft friction even more. Then there is the fact that animals aren't a consistent medium like foam. Foam also is also not a valid test medium for BH strength/integrity, so at the very least you would have to test BHs first and separately from other penetration testing.
My point is not that foam penetration tests are totally irrelevant. Just that it's easy to draw the wrong conclusions depending on many variables inherent in foam that are not nearly as important in living tissue and that many people don't consider.
Light arrow vs heavy arrow...both equal KE.
Since the lighter arrow is moving at a faster rate, it will travel further before the effects of friction take affect.
Larger diameter vs smaller diameter arrow...equal KE. Again the larger object will be effected by friction first.
The foam collapses around the arrow, creating friction and stops the arrow.
What is proven by Physics/math is that an object with more mass will take more energy to stop it. Ok, why then is the lighter arrow penetrating further...velocity of the arrow, not KE. Thus the reason foam is not a good indicator of arrow performance.
KE is lost at impact, momentum/mass is not...rules of physics tells you it takes more force to slow it down.
Can a 375gr arrow blow thru a deer or an elk, yes it can. As a 500gr arrow will. The reasoning behind a heavier arrow is more about deflection of the path of the arrow and the force needed to keep it on its path. A lighter arrow will be more challenged to do so then a heavy arrow....remember more mass requires more force to slow it down.
Lighter arrows loose more of its energy faster than a heavier arrow as distance increases. This has to do with the drag forces placed on the arrow, again mass takes more to slow it down. In a vast majority of hunting situations its probably a moot point.
I feel both KE and momentum can be used together to come up with the "perfect" arrow given ones bow setup.
If I have to make a choice, more likely I would go with a heavier arrow.
I am not sure how many times you are going to brow beat this website with that stupid phone book video which you consider the ark of the covenant with respect to arrow performance.....BUT I have seen evidence myself with respect to chronograph readings with 2 different weight arrows. Typically the heavier arrow will retain more energy as it is traveling faster relative to its weight. I don't care to try to calculate why even if I could as I will take the general consensus of bowhunters who have shot thick skinned game in that typically heavier is better. I agree with others as obviously there is a point of diminishing returns but in general heavier is better.
I look at the "why" for this topic the same way my father in law looks at the pythagorean theorum. My wife and I were helping him remodel a home many years ago when he was showing my wife how to determine if something is square with a tape measure. He told my wife that "all you have to do is measure 3, 4, 5" (meaning 3 units up one leg, 4 units up the other leg and 5 units at the hypotenuse). My wife said...."dad, that is called the pythagoreon theorum." He immediately looked at her and said "I don't know what in the hell it is called, I just know it works." :)
If given two options that I couldn't back out of, I had to choose one of the options. Shoot an Elephant with a 350 grain arrow out of a 100 lb bow or shoot an elephant with a 1000 grain arrow out of a 30 lb bow... I would take my chances with the former.
"The data indicates that an arrow whose mass is approximately 650 grains, shot from a 45 pound bow, penetrates heavy bone with a frequency virtually identical to a like arrow fired from an equally efficient bow of 55 or 60 pounds. With like broadheads, it is more likely to penetrate heavy bone than a lighter arrow striking with significantly greater impact force."
The theory is that the heavier arrow resists slowing better when it strikes heavy bone, and "it allows the arrow to exert whatever amount of force it carries upon the bone for a long enough period of time to breech the bone’s structural integrity."
Maybe the 1,000 gr. arrow out of a 30# bow would be a better choice?
http://tuffhead.com/ashby_pdfs/ashby%20ours/2005%20Part%206%20Update.pdf
A question for Purdue: if KE is as important as you claim (and I do appreciate some of your arguments), why are fishing arrows so heavy?
A question for Purdue: if KE is as important as you claim (and I do appreciate some of your arguments), why are fishing arrows so heavy?
Then you do not believe in the laws of physics.
Shoot the same weight arrows, one with a FT, dull BH and another with a sharp BH....then come back and explain your results.
I know of no credible broadhead design engineers that consider foam anything but a backstop that is really good at stopping arrows.
WRT foam emulation animals.... apples and oranges.
The salient point here is that foam and animals have very different properties, and using one as a proxy for the other to predict penetration is sophomoric.
Of course foam squeeze reduces penetration, but it does so with animals as well even though the blood and tissue liquids mitigate that squeeze. It is nevertheless a significant factor and that is one of the things that affects penetration in animals. This is why the micro shaft companies claim they get better penetration in actual hunting situations.
I do believe in the law of physics. i also believe in clear writing and for the life of me some of the above "arguments" are as clear as mud. Please try to write more clearly.
Is your point that a sharp broad head would reduce shaft squeeze and out penetrate the othes? If so, state it more clearly please, it's simply not clear what you mean.
Assuming this is the case, let's say a medium or low density foam produces 3xs the squeeze factor on arrows than in living tissue. That still doesn't mean a foam penetration is not informative in our arrow tests. In absolute terms the result may not correlate 1:1 with tissue, but in relative terms the results may give accurate correlations.
Shoot the same weight arrows, one with a FT, dull BH and another with a sharp BH....then come back and explain your results.
Pretty clear what I said...You shoot and come back and explain the results.
As I said before, understand the laws of physics, then apply.
No. Just saying it does not make it true. The lighter arrow will lose its energy faster than the heavy arrow. The two factors, initial speed and energy lose rate, cancel each other out. They will have the same penetration IF, IF, IF, the resisting forces are also equal. distance = KE / resisting force (per Sir Isaac Newton not me) It doesn't matter whether the KE comes mostly from mass or velocity.
"What is proven by Physics/math is that an object with more mass will take more energy to stop it."
NO, for the reasons above. I showed you Newton's math; where is yours?
"KE is lost at impact, momentum/mass is not..."
KE is lost at impact as to the velocity changes. Momentum is ALSO lost at impact as the velocity changes.
"....rules of physics tells you it takes more force to slow it down."
What rule of physics would that be? Remember, KE being equal.
That's true, but isn't it also true for velocity. Funny how everyone only looks at these formulas through a mass lens and never a velocity lens.
"But not necessarily individual areas of performance, penetration, trajectory, etc."
In flight archery (distance shooting), they prefer a VERY light arrow.
Some seem to imply that only a fast arrow melts foam. In the video it didn't appear to make any difference. Foam, phone book and gelatin, all the arrow had about the same penetration. Did the fast, light arrow melt the paper and gelatin too?
As good ol’ Sir Isaac Newton taught us, F=ma (Force=mass*acceleration).
KE is the product of its speed and mass.
Momentum is a product of its mass and velocity.
They are heavy for 3 reasons:
1.) They are heavy because they are usually made from solid fiberglass. :o)
2.) The frontal drag of an object passing through fluid is proportional to the square of its velocity. This is why a slow, heavy arrow has an advantage at long range. It has less frontal drag applied and thus retains it's velocity (therefore KE) better than a light, fast arrow. This phenomena is exaggerated when passing through the much denser fluid of water. Therefore, more KE is retained by a slow, heavy arrow and therefore better penetration is achieved. In my experience, this becomes a factor beyond a water depth of about a 9".
3.) The heavy fiberglass arrows are VERY strong and can withstand the violent thrashing of fish and alligators MUCH better that a light arrow. In my experience, this is the main reason for their use at the depths I shot.
Hide, bone and muscle are not a fluid. The lungs are, but the main fluid is air. The short amount of air that the arrow passes through provides only a negligible amount of frontal drag. Only on a bladder or possibly a stomach shot would frontal drag start to be an issue. And just because frontal drag increases exponentially does not automatically mean it is significant. It could mean it went from 2 oz. to 6 oz. of drag for a distance of 3". I have never calculated it, so I don't know what it is. I just know the faster arrow has more drag when passing through a fluid.
Shooting a FT and a dull BH into foam will give different results. Yet KE is the same, what changed? Surface friction....
What rule of physics would that be? Remember, KE being equal"
So you disagree with my statement then go on to say...
" This is why a slow, heavy arrow has an advantage at long range. It has less frontal drag applied and thus retains it's velocity (therefore KE) better than a light, fast arrow. This phenomena is exaggerated when passing through the much denser fluid of water. Therefore, more KE is retained by a slow, heavy arrow and therefore better penetration is achieved."
Purdue...so which is it?
OK let's use F=ma
We have a target that provides a consistent resisting force "F" of 1000. A light, fast arrow with a mass "m" of 200 and a heavy, slow arrow with a mass "m" of 400.
For the light arrow;
a=F/m = 1000/200 = 5 ...... this is the rate of its deceleration. Shorter time to stop.
For the heavy arrow;
a=F/m = 1000/400 = 2.5.... this is the rate of its deceleration. Longer time to stop.
IF they both had the same KE when they hit the target, then the heavier arrow would have also had less velocity than the light arrow. One goes slow for a longer period of time and one goes fast for a shorter period of time. The penetration is the same.
work = F x Distance = 1/2 mv^2 = KE
therefore: distance = ( 1/2 mv^2 ) / F = KE / F
If the two arrows have the same KE and the same resisting force, they will have the same penetration.
Nothing inconsistent in my statements. It only requires more force if you try to stop an arrow in a shorter distance or less time. Still waiting on the physics that explains your statement.
Anyone that has shot enough 3D has had that gunk gets stuck to your arrows.
Anyone that bowfishes can explain penetration. No sexy formula..its simple, more arrow weight = better penetration. I guess this really disappoints some of the quasi scientists is all I can figure.
I've said several times I'm not referring to the dense foam of animal targets. Maybe I'm the only one here who has soft foam targets, but regardless there is soft and medium foam out there and it is totally unlike the 3D animal target hi density. When I push an arrow through it with my hand, the consistent is pretty much like liver/muscle or say a watermelon. You cannot do that with high density foam such as is used in 3D animal targets and certain foam blocks. It's like saying all metal or wood has the same qualities. They don't.
It also seems some people here can't understand the point that even if friction is increased several times over shooting a live animal, the foam results of mass vs. ke or vs. momentum or testing other variables such as shaft diameter, bh type, etc. would still be applicable in relative results.
And I seriously doubt Chuck Adams had the last word on the usefulness of foam in penetration studies. Some people don't even like ballistic gel for penetration experiments and let's not forget that not all ballistic gels are the same.
The next time I shoot an elk that is under water I'll be sure to use a heavy arrow.
I answered David A's question above. Read it. Not much that's applicable to hunting.
So why wouldn't that also predict fast arrows would slow quicker upon penetration upon impact with hide/muscle/etc.
Thanks for your post re: fishing arrows. I wonder if another factor might be less arrow deviation from the influence of the trailing line?
All I know is that it's a Fluid dynamics formula that says drag increases at the square of velocity and hide, bone and muscle are not fluids. I therefore don't know why it would apply.
If drag increases more for a fast arrow in muscle, I would think that it would have shown up in the video's gelatin test. It didn't.
This topic, broadheads, and arrow weight should be lumped together in their own forum.
Water is the most prevalent molecule in meat (comprising roughly 2/3), which elk are made of - but it probably still does not occur to you why that is relevant.
sigh.... all else equal, equal KE as well.... at impact the heavier object resists the force more than the lighter object. The whole debate was comparing EQUAL KE and penetration. Not a 1000 arrow from a 30 lb bow nor a 350 from a 100 lb bow. I didn't even try to run the numbers but the KE is not equal.
That's not even debatable, it all comes down to how much trajectory you want to lose to shoot the heavier object. And how much penetration is needed to do the job you want the arrow to do. Deer, black bear, antelope etc.... medium game penetration is NORMALLY not a big factor with modern equipment. Trajectory may be more of an issue, depending on the archer.
Start getting into big game, elk,moose, etc.... and then farther into ridiculously big game.... then penetration can be an issue.
Just as it is when choosing a rifle cartridge to match up to what you are hunting.... how you are hunting it and where.... same goes with archery equipment. Match it to your needs. But don't even try to tell me it's all the same, all depends on KE. It's not... and it doesn't. Period.
"That's not even debatable"
Put in the context that this was intended, it is debatable. It seems that throughout this thread and many threads like it. Many people believe that a heavy arrow wins the penetration contest just by virtue of being heavy. As a response to a comment along those lines, The ridiculous extreme was used to easily illustrate that it is not necessarily so. Which also aligns with the original question regarding equal KE.
It is not relevant. What is relevant is wheather or not the commonly struck tissue acts as a fluid. A tree is about 50 % water. Do you see where I'm going or do I have to explain it further?
David A, "...since animal tissue is largely water and since frontal drag increases at the square of velocity, wouldn't be a significant part of solving the paradox as to why light/fast arrow may penetrate less on animals than heavy arrows?"
As I mentioned above, gelatin which is 90% ?? water and is accepted by most as giving a reasonable representation of tissue, did not show a significant difference in performance with either weight arrow.
I contend that there is very little fluid that the arrow encounters as it passes through on a double lung shot. What really matters is what percentage of the total resisting force is frontal drag. The controled test shows that it doesn't amount to much.
Do any of you worry about the energy robbing water when shooting in a light rain? You probably never even thought about it until now.
Probably that wood is a good proxy for arrow penetration tests because it has similar physical properties to foam, whereas the rest of us understand that arrows are slowed by wood and foam in a fundamentally different way than in flesh and that neither represent a good medium for comparison. Am I close?
If that's not enough to show you guys that you're wasting your time with this guy I don't know what is.
A grasping for straw attempt for an equation that will explain better arrow penetration in an animal [multiple densities].....when its right there in front of us- add arrow weight
Weight alone is important until you actually test it. Then you find out it doesn't mean squat. Test in phone books, gelatin, bologna, anything and post your results like I did. I know, it's easier and safer to just type.
The truth is out there and it will be according to the laws of physics although I also agree there are various issues that a simple application of physical laws may not cover. But it won't be because the laws of physics are broken.
I said "....energy robbing water". That would be the rain that the arrow hits with it's frontal area. Much of the effect of rain on trajectory is due to the downward force of it hitting the length of the arrow.
I'm curious, how much does rain affect the trajectory of your 3-D setup at 20 yards? Is a slow arrow or a fast arrow effected most by the rain?
" Am I close?"
Not at all. I was trying to show that moisture content frequently has little to do with wheather or not that item is a fluid. If it's not a fluid then the drag formula does not apply. Muscle is not a fluid.
David Alford, "But it won't be because the laws of physics are broken."
So true!
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As I mentioned above, the actual about of blood that an arrow encounters on a double lung shot is far less than most would expect. However, after the shot the lungs fill (at least partially) with blood. This space where air normally occupies would hold a far greater amount of blood than normally held in the lung's tissue. This blood could add a significant amount of resisting force to an arrow. As it coagulated the resistance could increase.
Ashby shot into just such animals. Could this account for some of his results? Yet another potentially significant variable in his uncontroled tests. Just something else you need to consider whenever you see tests conducted on dead animals.
