Sylvan:

What you are saying has logic behind it, but the way KE is usually measured tends to negate some of the types of energy that are being mentioned as wasted or non-directional energy. The KE is determined by chronographing the arrow. When this is done, the forward motion of the arrow is measured in fps. The Chrono does not measure rotational energy, vibration or any of the other wasted energy. Energy can be wasted upon impact as well as on launch. I don't really disagree with the idea of momentum being more important, but I'm not convinced that KE is really so irrelevant. I also think broadhead style is very important. I generally use an old bag target to shoot broadheads into. I can shoot Muzzy practice blades or Slick Tricks into the bag, and it stops them every time. If I put a cutting nose Phantom on the arrow, it sails clean through the bag in buries about 10 " of shaft into the ground. I do know quite a few guys around here that shoot Rocket Sidewinders (1.5"cut) from 60# bows, shooting carbons, and blow through the deer pretty consistently. That would not be my first choice if I wanted good penetration, but it seems to work for them.

Yes I am a retired research engineer with over 30 years experience in the labratory and it is interesting that you accuse me of having no common sense but yet it is you who are generating these bizarre Rube Goldberg scenarios with 40 pound arrows and it is me trying to get you back into the "real world" of archery. But I'll answer your question anyway.

I did not say your wifes bow would launch a 40 lb arrow 32.16 ft. I said that if it was aimed horizontally it would accelerate the 40 lb arrow at 32.16 ft/sec/sec and if it was aimed vertically the arrow would not move at all.

When you say a 40 lb draw don't you mean that the peak force for that bow is 40 pounds[/quote]

BTW I have been polite and curtious in my posts to you. If you don't agree with what I say that is fine but there is no reason to launch personal attacks.

JOE PA wrote: I agree with you Joe. That is why Ashby is not technically correct when he says that rotaional, vibrational etc energy is included in KE. Like you say, we measure only the forward velocity with the chronograph and then calculate KE=1/2mv^2. I also agree that KE is not so irrelevant. Once you have decided on your broadhead, the more KE you have the more it will penetrate.

BobCo19-65 wrote: Where do you get the idea that I feel superior. You must figure that if someone disagrees with something then they feel superior? I know I may sound a bit know it all "ish" and I appolgize for that but I don't appolize for being educated and knowlegeable in physcis and mechanics. I enjoy discussing archery mechanics and I thought the "technical" forum under "Bowhunting" might be a good place to indulge myself. Maybe I was wrong. It seems that too many here view personal attack as a valid form of technical discussion. Anyway, I would enjoy a conversation with Dr. Ashby. You would proabably be disappointed though. I disagree with him on only a minor point. Turns out that it was you who was arguing that KE has nothing to do with penetration. In his paper Ashby doesn't say that at all, but rather says it plays a very minor role when compared to the broadhead design.

So then in your scenario the draw length has nothing to do with it. Her 25 inch draw bow set at 40 lbs will accelerate the object exactly the same as a 31 inch draw bow will that is also set at 40 lbs. Hmmmm that's an interesting theory you have there

Yes I did but then all 40lb draw bows don't put off the same amount of energy do they? Doesn't cam design and draw legth play major roles in determining the amount of energy produced? Couldn't two 40lb pull bows produce considerably different amounts of energy?

You answered your own question

Sylvan
I have a few questions if you would. They are not a set up but things I would like to know from a physcis view.

1st In relation to some thing a HILLBILLY would understand what is 1 KE vauied to? [like a 8 oz wight droped?]

2nd I have the pc thing for calcuating KE it seems to take quite abit of arrow grs or puondage to rase ke alot. So to me this meens 1 KE is a lot?

3RD If my bow shoots an arrow at 297 fps and my arrow is 552 grs what would my ke be and what would my PEITRATION be? I have 3 difrant numbers for ke right now with the same numbers useing difrant calulaters.Why is this?

TY very much in advance
charles bradford

You are confusing acceleration and velocity and what I said is not my theory it is Newtons 2nd law of motion.

Of course but this doesn't have anything to do with what we have been discussing. We have been talking about heavier arrows being shot from the same bow all things being equal are more efficient and carry more KE. And the answer is...

KE = m/2 x (SE / (m + mv))**1/2

Not my opinion just get a book and learn it for yourself. It's clear that I won't be getting through to you.

ELKINMTCWB wrote: If you droped something that weighed 8 oz from a distance of 2 feet it would carry 1 ft/lb of KE at impact.

I guess that depends on what you compare it to. 1 ft/lb is a lot if you only need enough energy to move a postage stamp but it would be a pittance if you wanted to move a train with it.

That would be 108.1 ft/lbs of KE. I suspect the difference is in the value the different calculators use for the acceleration of gravity. Because grains is not mass it has to be converted and to do this you divide grains by 7000 becuase there are 7000 grains in a pound and then becuase pounds is still a force and not mass you divide again by the acceleration of gravity. This is a number kind of like PI you can carry it to as many places as you want for accuracy. Most use 32.16 but some use less or more decimal places. Unless you are getting really big differences I suspect this is the reason.

No I am not confusing anything. I am talking about the amount of energy produced. You said that a 40 lb bow would launch an object 32.16 feet. I merely pointed out that your calculation was bogus because there are other factos that go in to how far it could potentially launch an object because the two different bows will produce different amounts of energy and will therefore launch the object different distances (if they will at all which I do not believe they will). However we digress. I realize this is a different subject I just wanted to visit your proclamation and point out that it was infact invalid. Just trying to set a precedent here

That was before you boldly proclaimed how far a 40 lb bow would launch a 40 lb object. Which goes back to my point about you trying to use calculations to give you answers about real world scenarios and there inability to do so.

I said that 40 pounds would accelerate a 40 pound arrow at 32.16 ft/sec/sec now you are confusing distance with acceleration. I'm sorry but this discussion just isn't going anywhere.