Arthur P

There's the direct quote from Dr. Ashby's arrow lethality study. If you'd like to read it, the complete study - including graphs - is posted right here.

Sylvan

Thank you Arthur P. Well here the word direct is added and that makes a big difference from what was said earlier. Its a far cry from "...an arrow's Kinetic Energy tells one absolutely nothing about how well it will penertrate..." Although I think the statement that "KE has no direct bearing on penetration" is misleading it is not incorrect. Although it is true that KE is a scalar quantity while momentum is a vector quantity it is also true that as momentum increases so does KE and as momentum decreases so does KE so the implication here is misleading because he is also implying that momentum is THE indicator while KE plays almost no role. The tuning fork comparison is far from compairing 2 arrows shot from the same bow. I have yet to see an arrow carrying say 50 ft/lbs of KE simply stay in one position and vibrate! For all intent and purpose when refering to KE of an arrow it is a vector quantity.

Thanks for the link! I think you gave me this link once before but I was unable to open it. I don't have time right now but I will give it a try later. Thanks again!

Sylvan

silentassassin wrote: Actually 40 lbs of force acting on a 40 lb arrow will accelerate it horizontally at 32.16 ft/sec/sec and if by some miracle you could construct a bow that was capable of handeling both a 400 grain and a 40 lb arrow, all things being equal the 40 pound arrow would be propelled more efficiently than the 400 grain arrow. It would of course be moving much slower but it would carry more KE. Now insted of shooting the arrow horizontally you turned the bow vertical (this is what you are attempting to set up) you would still be accelerating the arrow at 32.16 ft/sec/sec but because gravity would oppose with an equal and opposite acceleration the net force on the arrow would be 0 so you are now doing what I said in a prior post. You have so exagerated the system that you are inadvertanly changing other factors and aren't compairing apples to apples. Your distorted scenario actually compares a 40 lb bow acting on a 400 grain arrow vs a 0 pound bow acting on a 40 pound arrow. When you stay in the realm of realistic conditions and only change the mass of the arrow, the more mass the more KE and the less mass the less KE. There is no getting around it!

Ratus

I still think you're Kevin S.

Sylvan

Just curious, anybody know what Dr. Ashby's degree is in?

Sylvan

Just curious, anybody know what Dr. Ashby's degree is in?

Sylvan

That was wierd!

Sylvan

ArthurP, Just finished reading Dr. Ashby's paper. Thanks again! When reading the paper in its entirety it is clear that he points out that neither momentum or KE alone are direct indicators of potential penetration. Without considering the arrow/broadhead combination you don't have much indication. I agree completely. My only issue with the paper is a minor one but I will point it out anyway as it relates to KE in this thread and of course because I find it "fun" to discuss such things! I think you and I tend to bore people with our technical blathering but here goes anyway...

Ashby writes: In the way we all refer to KE this is not correct. Like I said before when we talk about KE in an arrow it can be considered to be a vector quantity in that it is calculated from the forward motion of the arrow only. KE =1/2mv^2. The rotaional energy for example is not included but rather is "drained" from the forward KE as the arrow moves towards the target. The other "energies" that he talks about are the reason you have less KE as the arrow moves farther and farther down range. The total energy reamains a constant and is equal to what we normally call KE + these others. The "others" are not inlcluded in the KE number. They are of course all "present" and manifested in the arrow but are not included in the number we all call KE.

In the manner we talk of KE in an arrow a tuning fork KE would be 0 not a high value as Ashby says. A tuning fork has no forward motion so if you plug that in to KE = 1/2mv^2 you get 0.

I think a lot of the disagreement regarding these issues is a result of definition and context and of course sometimes people say things and they just don't know what they are talking about.

silentassassin

Are you an engineer because you sound like an engineer. A lot of knowledge on paper but no common sense. So let me clarify this since I am not as smart as you think you are. Are you saying that oh let's say my wife's bow set at 40 lbs and a 25 inch draw is capable of launching a 40 lb arrow 32.16 ft? Do you thing it is capable of launching a 400 gr arrow? I realize this is an excercise in futility because you aren't going to admit that you are wrong so we will both just have to settle for knowing that you are

PS I didn't say 40 lbs of force I said a 40 lb draw


The point was meant to be exagerated to emphasize the fact that there is infact a point a in which it will become less efficient. Several guys here have posted tests they have done verifying it. You might like to throw out mathemetical calculations that make your feel intelectually superior but at the end of the day that's why people roll their eyes when they here the word "engineer". That's because most of you guys don't have any common sense. You think there is a formula that can explain every real world situation and quite frankly there just isn't. I know that's the world you feel comfortable in but there just isn't a calculation for every real world phenomenon. I have done the testing myself but I didn't keep the data and I don't currently have the means of testing but maybe someone will jump in with some results they have verified for themselves though you have shown a propensity in the past for disregarding verified data that doesn't fall into line with your previously stated opinion.[&:]

BobCo19-65

Like I said, if you feel superior, why not take it up with the man himself. I'd love to see the conversation and it is very possible to do.