Arthur P

You still don't get it, bow hunter44. It's not the amount of energy lost to arrow oscillation that's doing this stuff. Here's the real deal...

The heavy arrow absorbs more energy from the bow because the heavier arrow has more inertia for the string to overcome before it can begin moving. It takes more of the bow's force to accelerate the heavier arrow than it does a light one. By the same token, it also takes more resistance to STOP the heavier arrow than it takes to stop the light one.

Since it's harder to stop,a heavy arrow isobviously going to penetrate further than a light arrow. Assuming all other things are equal, of course.

I swear, to me the whole thing is just ate up with the DUH factor, but folks insist on sticking to the KE thing. I just don't get it.

Dr. Ashby's studies have shown repeatedly that mass/momentum is a far better predictor of penetration potential than KE is. Regardless of how the physics books define the terms, it's MOMENTUM that does the trick.

Rogue

When discussing KE or momentum I think that we do have to take into account the average bowhunter. I figure I am about average (maybe slightly below), so what does it all boil down to for me. There isnt any doubt that with todays bows and a properly spined arrow that any north american game is in trouble. Here is my take, I like heavy arrows for the major reason that they are quiet. Since sound travels at approxamately 1100 fps and even todays bows havent achieved that yet, game will almost always hear the bow before the arrow reaches them. There for I will take my chances with heaver quieter arrows.



Bill

TFOX

5 pages has to be a record for you Arthur on staying out of the ke/momentum debate.

passthru79

Yeah obviously the heavier arrow has more penetration potential, but when we are talking about todays high energy bows will that heavier arrow make that much of a difference. Everyone keeps saying it can make a world of differance on a marginal hit, well will it blow through a shoulder that a lighter weight arrow wouldnt. I dont argue the fact that the heavier arrow will usualy carry more momentum and that momentum is the major factor in penetration. I just dont think it makes a heep of difference unless we are talking about extreme weight differences, like comparing a 200 grain arrow to a 850 grain arrow and shooting at a elephant. For most north american game I dont think it really matters.

Arthur P

Just got back online, TFOX. Had carpet layers in the house all day and had to get all the electronics out of their way before they'd get to work. Been having the DT's all day without my 'puter.

Passthru... considering the difference in point of impact between a 300 fps arrow and a 250 fps arrow at 30 yards is less than an inch, why not stack the odds in your favor as far as penetration goes and use the heavier arrow? The way I see it, it's better to have it and not need it than to need it and not have it. Like when you think you've gone out deer hunting but instead come across a big ol' 500 lb wildboar hog.... I don't know about you, but if I get a chance at a hog, I'm through deer hunting for the day.

bow_hunter44

I could have sworn that was the original argument... Momentum (in this case inertia as the object is moving, as opposed to inertia of a stationalry object which has no momentum) being the culprit that causes penetration of a projectile - not kinetic energy. Durr..........

Straightarrow

That the point, it really does matter. I've probably heard no less than 10,000 stories about how "my arrow didn't penetrate very far" and I've witnessed meager penetration on dozens of shot on TV hunting shows. All this is on tiny whitetails shot with 60-70 lb and higher draw weight bows. It helps not just on marginal hits, but in marginal weather conditions, marginal shot angles, when brush, twigs or grasses get in the way. It also helps when someone isn't smart enough to use a high FOC arrow, and it's light weight to boot. It helps frequently and it makes a big difference.

In fact, I've never seen anything so beneficial that is so resisted. The "need for speed" crowd appears willing to sacrifice so much to eek out a bit more speed.

Arthur P

Momentum doesn't cause penetration by itself. You can't have momentum without KE. You can't have KE without momentum. They're two sides of the same coin. What I said wasthat momentum is a better predictor of penetration potential than KE.

As said all thru this thing, KE doesn't change much, no matter how much arrow mass you use. Only a few foot lbs. But momentum changes a LOT. An arrow with twice the mass will have twice the momentum.

You need more penetration for a bigger, tougher animal, or just better than what you're getting with your current setup? Go heavier with your arrow weight. Change to a smaller diameter broadhead, fewer bladesor switch to a cut on contact style. Go with a smaller diameter shaft. (I always arguedagainst that theory, but Ashby's research is proving it out. Gotta go with the data instead ofgut feeling.[&:])

Another trend showing up on Ashby's current study indicates it's a good idea to go really heavy on point weight, because arrows with really high FOC's are showing significantly better penetration than arrows with 'normal' FOC's. Makes sense becauseincreasing yourFOC makes for more stable arrow flight. Probably works the same way inside a chest cavity.

Straightarrow

Arthur, my theory is that weight in the rear, tends to be deflected after the tip has entered the body, causing the rear of the arrow to not want to follow the tip. When the weight is on the tip and it hits something that deflects it, the tendency is greater for the light-weight rear to follow the tip. Now that I think of it, you're most likely correct. It is probably the same principle that allows the stable flight in adverse conditions of wind and twigs, etc. - resisting deflection forces.

bow_hunter44

I must agree, one cannot have kinetic energy without momentum (p), nor can one have momentum without KE. As they are both functions of mass and velocity, at zero velocity KE and p both equal zero. Also true, momentum does not cause penetration by itself. However, it is the major contributor – as you indicated, the greater the momentum, the more difficult it is to stop the arrow = more penetration. On the other hand, I’m a bit concerned about the math behind the argument “kinetic energy doesn’t change much no matter how much mass you use…. But momentum changes a LOT”. True, an arrow with twice the mass will have twice the momentum (at constant velocity, p = mv). But the same is true about KE, an arrow with twice the mass will have twice the KE (at constant velocity, KE = ½ mv2). On the other hand, an arrow with twice the velocity will have twice the momentum (at constant mass), but will have four times the KE (at constant mass). In other words, mathematically KE changes more dramatically than does momentum (momentum is a linear function but KE is exponential). Perhaps a small change in momentum has a dramatic impact on penetration? I would have to defer to Dr. Ashby for that.

On the other, other hand – weight on the tip vs. weight on the end, hmmmmm. If memory serves me correctly, (I once had a memory, I just can’t remember where I put it!), mass at the end of a projectile will ‘push’ the projectile into a target more (greater inertia on the end of the arrow) that mass at the front of the projectile will ‘pull’ it into a target. Using that logic, mass at the end of an arrow would create more penetration than mass at the tip. However, that is most likely the case on a projectile that can’t torque or deflect upon impact, as an arrow can. An arrow with a heavy end, upon impact, would likely deflect. The arrow would give up some of it’s momentum to deflection rather use all of the momentum for penetration. As such, the projectile (arrow) than deflects upon impact could have greater penetration than one with mass at the end. Not to mention, the FOC argument as it related to arrow flight that will also contribute to the total energy and momentum of the arrow when it reaches the target. That all sounds very similar to what Straightarrow said…

Mercy, a rather lenghty passage!!