I understand that both KE and momentum are linked, and cannot be separated when considering penetration. However, they are not equal measurements and they change in a disproportionate manner depending on whether one is concentrating on speed or on a non-deflecting arrow path.

Let me rephrase my prior example. If I'm trying to get the least amount of deflection, should I concentrate on getting my 300 grain arrow that flys 300 fps, up to 325 fps (a 17% increase in KE), or should I try to increase to a 600 grain arrow that flys at 230 fps (also a 17% increase in K.E)? I do not believe penetration would be equal, yet the increase in KE would be equal. The arrow with the highest momemtum will penetrate furthest when hitting a mixed media, where deflection is likely.

No, not yet. Do you like the Old Glory?

This is a much different example than before. We are now changing more variables than just the weight of the arrow. If we assume that your 300 ft/sec 300 grain arrow is shot out of a bow with 85 ft/lbs of stored energy, 65# peak, 30" draw, 8" brace, the stored energy would have to be increased to 99.9 ft/lbs to drive the 300 grain arrow 325 ft/sec. That also means a 11.4 pound increase in peak weight. If you are capable of storing nearly 15 more ft/lbs of energy and are able to shoot it accurately then I would say without question this is the way to go. At 75# though you shold increase the weight of the arrow to at least 375 grains. But of course now you are back to pretty close to 300 ft/sec but with more of both ke and momentum. See what I mean?

No, I'm not concerned with meeting manufacturer weight recommendations in this example.

The 300 grain arrow at 300 fps would have 60 ft/lbs of KE, just like in your example. I'm going to increase it by 17%, which would require shooting the same arrow 325 fps. Regardless of what draw weight is required, will it deflect equally when compared to a 600 grain arrow shot at 230 fps when entering flesh, hide and bone. I believe the lighter arrow in this example will deflect more. It will have the same KE as the heavier arrow, but it's momentum will be less. It's energy will be diverted off it's path more easily.

nodog, a lot of people don't think one can compare the equipment of yesterday to the equipment of today. Maybe there truly is no comparison between them, but I'll leave the ramifications of that thought process alone for now. That datamax character would have a field day with it.[:-]

At any rate, don't fall into the trap of thinking today's equipment is not subject to the exact same scientific principles that the old stuff was (and still is, for some of us). Again, a 350 grain arrow at 300 fps, generating 70 ft lbs of energy penetrates comparably to a 700 grain arrow at 150 fps and 35 ft lbs of energy only because of one reason.... The light arrow is going fast enough to equal the heavy arrow's momentum. At half the weight, it has to be shot at twice the speed and generate twice the energy to do the same job as the heavy arrow.

Look at all the things one has to do to get that 350 grain arrow to shoot 300 fps. Extra hard pulling cams, high draw weight... Do you realize that some bows today with 70 pounds peak draw weight store upwards of 90 pounds of energy to be released to the arrow? Know how those 90 pounds get into those limbs? That's how much weight you've actually drawn to get your bow to anchor. Peak draw weight is decieving in that way. You think you're only pulling 70 pounds, and that's what the scales read when you measure the draw weight. But with today's cams that hit peak early and maintain it until very close to anchor, that peak weight stays up there a l-o-n-g distance when you're tugging on it. Honestly, my shoulders can't take that kind of draw cycle, but it allows someone to shoot an inefficient, ultra light arrow with enough force to kill medium size game - if they make smart decisions on the size and type of broadhead they use and - naturally - have the bow tuned to perfection.

With a recurve or longbow, the weight comes up gradually until you hit peak at anchor. They store far less energy to be release to the arrow, so people have to use heavier, very efficient arrows when hunting with them. Those relatively heavy, efficient arrows, shot from bows that have limbs that store much less energy, allow the traditional archer to achieve exactly the same performance on game as the guys with the dinky little arrows, and do it with much less KE. How can one explain the same performance with less KE? Quite simply, regardless of what some engineers say, KE is not a very good indicator of penetration potential. Momentum is. And I'm quite certain there are a number of engineers that would confirm my point of view.

I really don't want to sound like momentum is the end all, be all because it's not. In my not-so-humble opinion, it's simply more important than KE. Even then, it's merely one part of the whole package. The size and type of the broadhead, number of blades and blade sharpness pretty much dictate how much energy and momentum you're going to need when it comes to pushing it through an animal's chest cavity. And that arrow must be flying straight and true to make the best use of it's energy and momentum.

To Sylvan... We definitely have some communication problem. The sky is blue in my world. How 'bout yours? [8D] Saying the 600 grain arrow is the same 600 grain arrow is definitely true. I just can't grasp the logic that prompted the statement. I don't see how you can say the paltry increase in KE is more important than the much larger increase in momentum when they are both attributes of the same arrow! It's a no brainer that the arrow will penetrate exactly the same amount as itself.

Arthur,
I was with ya every step until here buddy! NOWHERE did I say ke was more important. NOWHERE did I say momentum was more important. I have continuously said that ke and momentum are inseperable in archery. You are the one obssessed with trying to convince everyone that momentum is more important. I have continuously said that the argument is not even usefull. It amazes me how you continuely twist what I say and continuously miss the point.

IT IS A NO BRAINER that in this example they are both attributes of the same arrow. The point is that in the example the 17% increase in ke is of EQUAL importance as the 52% increase in momentum. Neither could be more important as you have so adroitly pointed out, " It's a no brainer that the arrow will penetrate exactly the same amount as itself. " The increases in ke and momentum are in your words "...they are both attributes of the same arrow". We finally agree! I think we agree most of the time but you seem to have a tendency to "invent" ways that we disagree. But of course saying the increase in ke in this case is "paltry" and the increase in momentum is "much larger" doesn't mean anything does it? The result is the same! Just for fun, let me twist your words a bit. You said that it only takes a "paltry" increase in ke to achieve the same increase in penetration as a "much larger" increase in momentum. Therefore momentum is less important. Now is that fair?

BTW, the sky is blue and white here today!

One last thing KE is by definition the distance an arrow can push with a given amount of force. Momentum is by definition the time an arrow can push with a given amount of force. If you can find me an engineer who says that Ke is not a good indicator of penetration potential I will show you an engineer who flunked his mechanics course! Now I didn't say that KE was more important!!!! In fact in my opion both ke and momentum concerns are allmost foolish in light of broadhead desighn, sharpness, tuning etc...

I have a question. How far will an arrow carrying 0.6 pound seconds of momentum penetrate a material that resists penetration with a continuous force of 50 pounds? Answer is that it is not solveable without going back to velocity. You don't have enough information.

Another question. How far will an arrow carrying 50 ft/lbs kinetic energy penetrate a material that resists penetration with a continuous force of 50 pounds? Simple, Answer 1 foot!

But of course KE is not a very good indicator and momentum is! Obvously it all depends on what the question is.

Straightarrow, I understand what you are getting at, and you are not incorrect from a pure momentum/ke perspective. I have said on several occasions that energy as a result of high mass rather than speed is better for maintaing path and "breaking" through bone. But the choice you present is IMO not properly stated. You are implying that the archer is makeing a simple choice between KE and momentum but that is not the case at all. It's not like my case which changes only the weight of the arrow. The real decision you present is do I go after more penetration potential by increasing the stored energy in my bow or do I go after it by putting on a heavier arrow. This isn't a momentum/ke decision. If you can store more energy then you should do that first. The decision to pull more weight should have nothing to do with anything other than your physical ability to control it accurately. The more potential energy you have, the better off you are. You can always put on a heavier arrow too if you want even more penetrating potential.

Thanks for the history stuff. I always find archery history interesting. I once read that the typical draw weights on indian bows at the battle of the little big horn were 90 to 100 pounds. I think the biggest difference between then and now are the archers. Back in time little boys grew up shooting a bow. Sometimes there life depended on how good they were. They shot them all the time. Much of Englands success in battle depended on the prowess of its archers. Draw weights were incredibly high relative to today's archers. Very few of us could draw the bow of a boy from prior era's.

Woohoo hehe I shoot a 90# to 100# mathews safari. I like a heavy pound bow.

My example was to show that if you equalize the KE of each arrow, that the heavier one would penetrate more. If the variable of kinetic energy is eliminated from the equation, and yet the heavier arrow pentrates further, then why?