I understand what you say Len, and how you read it, but it still makes sense to me. I think that he wanted to show that arrows with equal momentum at the point of impact, one being light and fast, one being heavy and slower will not have equal penentration. Therefore equal momentum at the point of impact does not equal penetration because of increased tissue resistance for the light, fast arrow.

I wish we could have gotten him over here, to clear things up, but he is now doing some research in New Zealand.

IMO, to the archer the diffence between KE and momentum is purely an academic one. There is absolutely nothing you can do to increase KE without increasing momentum and of course there is absolutely nothing you can do to increase momentum without increasing KE. They move together inseperable. Again, after ruling out a new bow or doing more work and to a much lesser extent lowering virtual mass (but no need to talk about that now), the only way the archer can influence KE/momentum is by changing the weight of his arrow. Heavier means more KE/momentum but the price is a bigger arch in trajectory. Lighter means flatter trajectory but the price is less KE/momentum. The tradeoff is between trajectory and penetration. It is not possible to choose between trajectory and KE vs. trajectory and momentum. For "practical" reasons the typical archer can forget the terms KE and momentum and simply substitute penetration. You're right Cougar Mag "To heck with KE formulas and theories" !!

Now how to choose. Basically there is a balancing act to be done here. If you want flatter trajectory you can go lighter and lighter but there comes a point where you will damage your equimpent or you will not have sufficient penetration to dispatch the animal and gain only a tiny flattening. If you go heavier and heavier there will come a point where you are only wasting the penetration capability by driving the arrow deeper into the ground on the other side of the animal and making distance estimation unnessisarily more critical.

Is there an absolutely correct balance? If you stay away from the extremese then NO! But I agree with walks with a gimp in that its probably a good idea to err on the heavy side.

Is anybody else having trouble posting?

Arthur,I said in SOME instances where friction is applied that faster arrows may have SOME advantage.NOT all instances,like on bone hits where there is more force applied to faster arrows.Thats why one formula doesn't work for ALL instances because of those variables we so often speak of.


When utilizing pure momentum,friction is kept at it's absolute lowest by using cut on impact 2 blade broadheads.Very few traditionalist choose 3 blade heads,some use 2 blade whith bleeders but those are really just 2 bladers with very small bleeders.Why not choose 3 blade heads if momentum is king.(bigger hole and more blood)Because the heavy,slow arrows can't push 3 blade heads as easily and they can't take that risk because speed and ke is low. You know there is more to penetration than momentum.Speed is the one factor used in both ke and momentum and speed can HELP in some instances.We know some manufactuers reccomend speed with their mechanical heads.They say to help spring their heads open but MAYBE to help fight off some of the friction encountered.Even your SMALL test on this board showed that people using a little more speed seemed to have better results with mechanicals.These statements are more for the sake of argument than as as factuall statements,although I do feel they hold some merit.

Targets that stop arrows by friction show that arrows carring more speed penetrate deeper.These targets are not animals and do not represent animals but at times when traveling through an animal,friction on the side of the arrow is encountered and it helps. I have stated this before and just to remind some what kind of friction I am speaking of.When you slide a heavy piece of steel across a table it starts out very hard but as it gets moving,the speed increases and the block gets easier to move.This is an actuall law of physics and friction.( as speed increases,friction decreases)This is a law of dry friction and I know you believe we are using lubricated friction in animals but I don't believe the arrow is ALWAYS lubricted.


As I have ALWAYS said,choose arrows based on your setup and spine instead of worrying about numbers on paper.Kinda what started this thread.A properly spined hunting arrow has already had the math figured for you.Not always does a heavy arrow penetrate better than it's lighter counterpart.Those variables again.


If I choose to hunt animals where heavy bone contact is probable then I would choose a heavier carbon or carbon/aluminum composite,but still wouldn't choose an aluminum.On deer,I choose ACC's because I get the same results with much lighter arrows.


Arthur,you know I am not a speed freak from past discussions and I am shooting 6 grains per pound on deer but that equates to 380 grain arrows for me. 250 fps is what I am down to now but that is is just an innocent bystander.[]

TFOX, you never heard of Snuffer broadheads or Wensel Woodsmans, I guess. Muzzy broadheads were designed by a traditional shooter. I've still got a couple packs of old 160 gn Muzzy Matadors in my box. A lot of traditionalists use 3-blade heads. I guess most don't for the same reason I don't. I can't get cut on contact 3-bladers as sharp as I like for hunting. Another reason I use 2-blade heads is I can get a half dozen for $20 instead of 3 for $30, and they do a perfectly good job.

Now, the guys shooting lighter draw weights (<50 pounds), yeah, most of 'em use 2-blade heads and better penetration is the primary reason. They don't have much KE or momentum to work with.

As far as speed and friction, you are totally incorrect. It's a plain fact that the faster something is moving, the more friction is generated. It's inescapable. Your physics problem about moving the block along the table and it getting easier to move as it speeds up, that is the concept of applying force to overcome inertia and generate velocity. It does not take friction into account.

Say a Piper Cub plane is flying along at 100 mph. Wind resistance (air friction) won't hardly warm it's skin. An SR71 Blackbird flying in excess of Mach 3, it's skin will heat up to over 1200 degrees. It's an exaggerated example, for sure, but I use it to illustrate the point. Increased speed, increased friction.

Ever heard of the term 'terminal velocity'? It's the fastest rate something can fall. It happens when an object's speed increases just to the point where wind resistance (friction) is equal to the object's weight. It can't fall any faster because the air won't let it.

Wind resistance is why all arrows lose speed, energy and momentum between the bow and the target. Assuming all else is equal except arrow weight... A lighter and faster arrow will leave the bow with more velocity but less KE and momentum than the heavier arrow. It will expend a greater percentage of it's velocity, KE and momentum while traveling between the bow and the deer than the heavier, slower arrow will. Reason is the faster the arrow is going, the greater the wind resistance. The greater the wind resistance, the more energy it has to spend just cutting through the air. It will have less KE and momentum when it begins penetrating the hide of the animal. Because of it's speed, it will encounter a greater percentage of resistance from the animals tissues than the heavier arrow will. All of which means it will not penetrate as deeply. Again, all else being equal.

Back in my field archery days, I found I actually had better long range trajectory on the 60, 70 and 80 yard targets with heavier 2216's than I did with 2213's, but slightly better short range trajectory (40 yards and under) with the 2213's. There was right at 100 grains difference in arrow weight between those two and, with the lighter tips on the 2213's, they had practically the exact same FOC. The 2216's simply carried better downrange.

You know how I feel about testing penetration in foam and thinking the results would be the same in flesh. Completely different media so they cannot be directly correlated. But let's run with that for a bit. Generally, when you talk faster arrows, you're talking carbon vs aluminum. So, you're almost always talking a smaller diameter. Smaller diameter = less surface area = less friction. In a target that stops arrows by friction, heck yes the smaller diameter arrow is going to penetrate deeper. But, why have they come out with easy pull targets? Why have so many 3D shooters been forced to carry heavy duty arrow pullers and arrow lubricants on their quiver belts? Because all that excess friction generates heat and melts those little carbons into the targets and they're hell to pull!

Would the smaller diameter help offset some of the friction on the shaft caused by the higher speed? According to Dr. Ashby's research, yes. It does. But still, as I mentioned before, it's the broadhead that bears the brunt of the resistance during penetration.

Now, comparing the penetration - in styrofoam blocks thick enough to keep the arrows from coming out the backside - between my unweighted Gold Tips at 460 grains and the ones I've weighted up to over 700 grains (from my compound, since my draw length varies from shot to shot with my stickbows, which would vary KE and Momentum from shot to shot), the heavy ones do penetrate about 2" deeper. When you compare apples to apples, things don't work out to fit your preconceptions. I wish I could get broadheads to fly good enough with my carbon arrows to compare broadhead penetration in foam with my regular and weighted arrows. Unfortunately, they won't fly straight with broadheads. But penetration in foam is all some people tend to believe.

Actually, weight (mass) is THE OTHER factor used in both ke and momentum formulas. Surely you didn't think I'd let you slide on that'n, didja?

But, yes, increasing speed of a specific arrow will help, because it increases both ke and momentum, ke more than momentum because speed is squared in the formula. On the other hand, speed can also cause problems since it also increases friction and resistance. But then, when you're talking about shooting the same bow without increasing draw weight, speeding up the arrow means going lighter in arrow weight. Which, in turn, reduces KE, reduces momentum and increases resistance. Three strikes against it.

But, to let you off the hook, most guys these days are shooting enough poundage to generate gobs of KE (and momentum by default) to blow through deer on well placed broadside shots, in spite of their light arrows. IN SPITE OF, not because of. Like I said earlier, most of them are getting more energy from their little twigs than old time bowhunters were using to take elephants. Elephant bows for deer! It's the equivalent of loading a .458 Winchester mag with 150 gn bullets for deer hunting. Sure it would work - well, assuming the rifling could stabilize such a short, light bullet - but the beating you'd take from that monster! Anyway, I'm not worried about those guys. I just hope they're smart enough to use heavier arrows if they go after bigger game. Even rifle hunters use heavier bullets designed with thicker jackets for moose than they do for deer, for the same reason - better penetration

It's the folks who are NOT shooting high poundage bows and are not generating gobs of KE that I'm trying to get through to. IMO, they need to follow Cougar Mag's lead and use proportionally heavier arrows. Not just for simplicity's sake though. They actually need to, in order to maxmize their KE and momentum.

If the assumption is that your arrow is faster because you put on a lighter arrow than you had before then the ONLY advantage is a flatter trajectory. The faster arrow in this case caries less of both momentum and KE. It will not penetrate as well as the heavier arrow. The only argument here is whether or not KE or momentum is a better predictor of the depth of penetration. By definition, KE is the integral of force of distance while momentum is the integral of force over time. Conventional thought in mechanics is that momentum is a better predictor of whether or not a projectile will penetrate or bounce off an object while KE is a better predictor of the depth of penetration if penetration occurs. So on game this becomes a pretty complicated thing as you are not penetrating a homogeneous material. But I will point out again, that the archer can not choose other than arrow weight and from that both momentum and ke move together. Again, the choice is between trajectory and penetration the rest is academic.

BTW, good explination Arthur P!

editing... Actually some argue there is another advantage to putting on a lighter faster arrow and that is that you will reduce the time the arrow is in contact with the string during acceleration thereby makeing the bow a little more forgiving to shoot. Same idea as the longer brace height lowers that dwell time. IMO this effect is tiny and probably not even noticeable to the typical archer.

thanks arthur, i declined out of flabbergastedness, and its the first time i've actually heard laws of physics being made up out of thin air to support someone's point.

Ya know, gibblet, the heck of it is that you have to dive off into fluid dynamics and thermodynamics to get the rules for a lot of this stuff. I certainly get in way over my head sometimes, cuz I ain't no nerdy mathmagician, but basic physics don't get the job done. [&:]

There's another point where I see a huge fallacy. I agree that any effect would be minimal - if even discernable. Even though time is slightly reduced, the distance the arrow remains on the string remains the same.

As for time, let's compare a 250 fps arrow with a 300 fps bow. Assume a 30" draw with a 7" brace height. About average brace these days, isn't it? You're left with a 23" power stroke. Of course, these numbers aren't going to be exact, because we're not figuring in the arrow's inertia on the rest and time the string takes to overcome that inertia.... So don't jump my stuff about it!

The 250 fps arrow will be off the string in 76/10,000 ths of a second. A 300 fps arrow will be off the string in 64/10,000ths of a second. I just don't see a whole lot of forgiveness in 12/10,000ths of a second.

Factor in the reflexed risers manufacturers have gone to in order to increase arrow speeds, and how easy they are to torque, I see no forgiveness advantage, whatsoever. There's a reason I prefer deflex risers, even though they can't shoot an arrow as fast. They're extremely hard to torque and ultra forgiving. Darn shame there are so few made any more.[&o]

Why Arthur P, I would never "jump your stuff" about anything! I know you wouldn't mine either, right?

Actually I agree with you. I was just raising the dwell time thing because that's usually what somebody comes back on me with when I say the ONLY advantage to a lighter faster arrow is trajectory. You can see from my post it was an after thought. Back to the time thing though in terms of percentage change in dwell, by your numbers 12 out of 76 is nearly 16% reduction in time. Although I still agree with you 16% has a much different ring to it than 12/10,000ths of a second.

Of course not!

I responded to that statement because I've seen the same thing on the forums and wanted to get in my 2 cents about it. [&:]

Sorry about that, I edited my post before I saw yours! BTW, I hear what you are saying!