Momentum vs K.E.

[rocky]

The arrow achieves maximum acceleration as it leaves the string at that point it begins to lose velocity as it move downrange. Therefore both momentum and Ke begin to fall. The factor that affects penetration at 5 feet is more about flex of the shaft than either Ke or momentum as the flex directs some of energy away from the direct path.

The thing about momentum is that the heavier arrow will maintain its energy longer than the lighter arrow even when penetrating a viscous material.

Too many folks go overboard in regard to both momentum and Ke, the real trick is to find an arrow weight that allows both a reasonable speed and a reasonable mass so that the arrow is able to better withstand outside influences on its flight and maintain enough energy to fully penetrate the target animal while giving the flattest trajectory possible.

Now if everyone limited their bow shots to 10 yards all this wouldn't matter much.

So, even though the shaft has a higher K.E. and Momentum measurement immediately off the string, more of that Momentum is directly behind the point after the shaft straightens out, which in my mind would at this point have more penetrating potential.
Am I thinking correctly?

[Mike Javi Cooper]

Momentum is the product of the mass of an object and it's velocity.
Mass x velocity is the formula we use to determine Momentum.
Got it.
Do you think that 'time of flight' has any effect on penetrating potential, even though by our system of measuring, K.E. and momentum start decreasing immediately?

Yes, the longer the arrow is in flight the less speed it has, so both momentum and Ke are lessened. So energy is lost and therefore penetration potential is lost.

[Mike Javi Cooper]

So, even though the shaft has a higher K.E. and Momentum measurement immediately off the string, more of that Momentum is directly behind the point after the shaft straightens out, which in my mind would at this point have more penetrating potential.
Am I thinking correctly?

Yes. Take an arrow with a broadhead on it and push it into a target block with the point directly in line with the direction of travel. Then repeat with the point at a 45 degree angle to the direction of travel, this will be a gross example of the issue as an arrow flexes in early flight.

[rocky]

Yes, the longer the arrow is in flight the less speed it has, so both momentum and Ke are lessened. So energy is lost and therefore penetration potential is lost.

As you said, the flex of the shaft directs energy away from the direct line of flight, wasting the momentum that would aid in penetrating potential, but once the shaft lines out, the momentum would be used more efficiently for penetrating potential, even though actual momentum is less.
Right or wrong?
.

[Mike Javi Cooper]

As you said, the flex of the shaft directs energy away from the direct line of flight, wasting the momentum that would aid in penetrating potential, but once the shaft lines out, the momentum would be used more efficiently for penetrating potential, even though actual momentum is less.
Right or wrong?
.

Sort of.. Think of it this way...

Momentum is energy with direction. Anything that uses up that energy is costing you penetration. The fact is that an arrow which does not hit its target with the shaft in line with the direction of travel is going to require more of the stored energy to be used. However the same thing occurs with broadheads that have a steeper angle than another. It simply requires more energy or force to penetrate, the momentum drops more abruptly as the expended energy increases.

I'm still not sure how this is momentum vs Ke.. both very different ways to define energy.

[hogdaddy]

i'm convinced that a lot of the lack of penetration some see with light arrows is due to sorry arrow flight combined with big mech. heads. on one hand you see people short on pounds, draw length, and arrow weight blowing through animals. they usually end up over spined with lots of grains per pound, lots of FOC. realizing their limitations use COC heads and are careful about shot selection. good things happen

on the other hand just watch TV lots of over bowed under spined gorillas shooting big mechs.at some inexcusable shot angles can't get a pass through at 15 yds. same people blow through bucks at 50 yds.
why,because the arrow has stabilized.

arrows matter spine, weight, foc, hielical, etc all matter IMHO

[JW]

i'm convinced that a lot of the lack of penetration some see with light arrows is due to sorry arrow flight combined with big mech. heads. on one hand you see people short on pounds, draw length, and arrow weight blowing through animals. they usually end up over spined with lots of grains per pound, lots of FOC. realizing their limitations use COC heads and are careful about shot selection. good things happen

on the other hand just watch TV lots of over bowed under spined gorillas shooting big mechs.at some inexcusable shot angles can't get a pass through at 15 yds. same people blow through bucks at 50 yds.
why,because the arrow has stabilized.

arrows matter spine, weight, foc, hielical, etc all matter IMHO

Well said. If a person is gonna go light it better be fkying perfect. Of course we want that on 600 grain arrows as well but on a 350 grain arrow it can be amplified even more. And I do not, will not shoot a hunting arrow without atleast 6 degrees of helical. Thats what I put on my blazers. Feather I shoot even more. Stable, straight, proper head. Good things happen as you put it.

[hogdaddy]

yes, its the system working together. helical is the closest thing to a magic bullet there is, it helps clean up any flaws in the system including mine like nothing else can.

[rocky]

Sort of.. Think of it this way...

Momentum is energy with direction. Anything that uses up that energy is costing you penetration. The fact is that an arrow which does not hit its target with the shaft in line with the direction of travel is going to require more of the stored energy to be used. However the same thing occurs with broadheads that have a steeper angle than another. It simply requires more energy or force to penetrate, the momentum drops more abruptly as the expended energy increases.

I'm still not sure how this is momentum vs Ke.. both very different ways to define energy.

i'm convinced that a lot of the lack of penetration some see with light arrows is due to sorry arrow flight combined with big mech. heads. on one hand you see people short on pounds, draw length, and arrow weight blowing through animals. they usually end up over spined with lots of grains per pound, lots of FOC. realizing their limitations use COC heads and are careful about shot selection. good things happen

on the other hand just watch TV lots of over bowed under spined gorillas shooting big mechs.at some inexcusable shot angles can't get a pass through at 15 yds. same people blow through bucks at 50 yds.
why,because the arrow has stabilized.

arrows matter spine, weight, foc, hielical, etc all matter IMHO

Well said. If a person is gonna go light it better be fkying perfect. Of course we want that on 600 grain arrows as well but on a 350 grain arrow it can be amplified even more. And I do not, will not shoot a hunting arrow without atleast 6 degrees of helical. Thats what I put on my blazers. Feather I shoot even more. Stable, straight, proper head. Good things happen as you put it.

yes, its the system working together. helical is the closest thing to a magic bullet there is, it helps clean up any flaws in the system including mine like nothing else can.

These posts summarize my thread.
I have guys come to my shop touting K.E. and/or Momentum theories for their choice of arrow build/weight.
There are other ingredients to consider when trying to achieve penetrating potential for each individual set-up.
Some of the newer bowhunters get confused when one guy touts K.E. and another argues Momentum, so they try to build an arrow to fit "what I read on the internet", and don't accomplish a darn thing because their arrow doesn't stabilize adequately.
Javi, I may not have asked the question exactly right, (K.E. vs Momentum) but I hope my point educates some of the newer bowhunters.
Both are a measurement of energy, and penetrating potential, but other aspects such as arrow flight are just as, or more important.

[JW]

yes, its the system working together. helical is the closest thing to a magic bullet there is, it helps clean up any flaws in the system including mine like nothing else can.

Yep. And I only know of one Randy Ulmer.

[hogdaddy]

not sure where you're going with that, does seem that you, i, and Randy Ulmer do agree on helical. none of us discovered it though, rather most have forgotten it in a world of center shot bows with drop away rests.

been an interesting thread. good hunting.

[JW]

not sure where you're going with that, does seem that you, i, and Randy Ulmer do agree on helical. none of us discovered it though, rather most have forgotten it in a world of center shot bows with drop away rests.

been an interesting thread. good hunting.

I was talkin about guys with awesome consistant form.

[hogdaddy]

ok i got you. yeah i need all the help i can get.