Badger_Girl93

Well, since Momentum = MASS x VELOCITY, we see that there is a direct linear relationship (is that the correct way to say it?)

So as long as yourLOSS of speed is not greater than your GAIN of mass, you shouldn't be losing any momentum. I think the only way to know for sure would be to test different broadhead weights out of your bow, and see how much the speed changes. When you do the math, make sure to have all the units of measurment straight. If you use grains and fps, there will like be some type of conversion factor. I think using kilograms and meters/sec would get everything straight...I could be wrong...just speculating here.

TexasBowHunter

Jeff,
You will be suprised that your KE and momentum will rise with the added weight without a huge amount of velocity loss. MECHDOC did some calculations with that Ontarget2 program he has and I have been playing with them, I will be building a few different weight arrows next week and getting hard numbers to compare to the program. If the program is accurate (which I have been told that it is pretty close) I will be going from a 380gr at 74 ft lbs KE to a 500gr arrow at 81 lb of KE with a considerable increase in momentum as well...Yes I am loosing a little velocity but not too much.

brucelanthier

25 grains probably is not going to slow it down much at all. I changed an arrow by adding 70 grains to the total weight and the speed only slowed by 13fps.

GMMAT

I guess this was the brainchild behind my post.

BobCo19-65

Ask this guy about momentum.


CLICK_HERE!!!

jackflap

So, as I stated imy situation in my previous post, are you saying the penetration capability is thesame since the KE is the same?

This is not a rhetorical question? I really don't know or even have an opinion at this point. But I listen and learn from the KING.

Germ

The King blows, winky winky

HuntingEd

Jeff think about it this way:
Energy is the ability to do work, which is force times distance (F*ds).
Momentum is defined as mass times velocity (m*v).
Mr Isaac Newton discovered in his second law of motion that force is equal to the rate of momentum change with time, F=m*dv/dt, for constant mass. Now since distance ,ds, = v*dt, and incremental KE of motion = F*ds, then substituting, KE= (m*dv/dt)v*dt = m*v*dv. Integrating , KE=1/2m*v squared.



In other words. KE ismore important!!

Think about this, you have 1000lb truck moving at1 f/s, and a 1 lb baseball moving at 1000 f/s. Which would you rather get hit buy??

I hope you answered the truck.

Momentum Truck = 1000
Momentum Ball = 1000

KE truck = 500
KE Ball = 500,000!!!!


Now take this to an arrow and its purpose. How does an arrow due its damage? It CUTS during penetration. IT doesnt create damage through blunt impact like a bullet.

Higher KE gives you Higher penetration because KE is ability to do work (ie. damage),

IMO, I'll take more KE because it gives you more energy to cut through bone and tissues. Becase I rarely make a perfect shot between the ribs.


Do a test. Shoot a 100 grain tip at your target. then a 125.

See which one penetrates deeper, it will be the one w/ more KE.

You also need to take into account that more mass increases the storage of energy the amount of energy you bow can produce doesnt change, so a lot of energy is lost on a light arrow due to noise, vibration etc. So more often than not a heavier arrow will have higher momentum & KE because of this.

But you then trade off the ablity to shoot flat! So its personal preference.

BobCo19-65

Heck, not even all Momentum is the same as it concerns penetration.

Excert from Dr. Ashby:

ALL MOMENTUM IS NOT THE SAME

Given two arrows, identical in shaft and broadhead materials and profile, and having EQUAL momentum, but possessing UNEQUAL mass, the arrow deriving the greater portion of its momentum from its mass will penetrate better. The Laws of Physics requires this to be true, andALL of my field test data validates this to be the case.

To say this in another way, arrow momentum derived through increasing arrow mass results in a greater gain in penetration than does momentum gained by increasing an arrow’s velocity. This is true because the tissue’s resistance is increased by the square of the velocity.


Let’s look at two arrows of equal momentum, but unequal mass, both of which expend all their available net force in the tissues. If the momentum is equal between two arrows at impact, the one with the greater mass has to be traveling at a slower velocity. As shown above, the slower arrow will be met by a lower resistance force than the faster arrow.

With the momentum of the two arrows equal at impact, their disposable net force will be equal, but the resistance force will be greater upon the faster arrow. Because of the higher resistance force, the faster/lighter arrow will lose velocity more rapidly, and its momentum will diminish at a faster rate than that of the heavier arrow. It will stop in a shorter period of time, thus it will have a lower impulse of force than the heavier arrow.

Full article here for those interested:

CLICK_HERE

JoeRE

Looks like we found one of those ill-informed illiterate dumb arses thar. I have said it before, KE is a traditional measure of projectile motion and works very well for bullets where transfer of energy is important (tissue damage through shock). Momentum is more important in my opinion to archery since we are talking about a heavier object that penitrates by slicing (cutting, ie energy transfer is not important) and momentum is simply the resistance of an object to change in motion. The more momentum, the more resistance it takes to slow and stop an arrow. You want better penetration, you either increase momentum (directly or indirectly) and/or switch to something that has less resistance (a cut on contact BH with a low cutting angle, for example)

Can KE be considered important? Absolutely...it almost always is sufficent, but if you want to get down to dotting all your i's and crossing your t's then momentum will tell you more about your archery setup