Momentum vs K.E.

[rocky]

I see both as a measurement of penetrating potential.
Explain the difference so that I can understand.

[BTLowry]

I found this

http://www.tuffhead.com/education/formulas_momentum.html

[Bowhunter1994]

go shoot a animal with a 400 grain arrow and go shoot another animal with a 600 grain arrow and see which arrow is harder to find... lol

[muzzlebrake]

Get hit broadside with a VW and compare that to getting hit broadside with a Semi. You might survive the VW hit even at 70mph. Not likely with a big semi weighing 80K.

[rocky]

go shoot a animal with a 400 grain arrow and go shoot another animal with a 600 grain arrow and see which arrow is harder to find... lol

Get hit broadside with a VW and compare that to getting hit broadside with a Semi. You might survive the VW hit even at 70mph. Not likely with a big semi weighing 80K.

I guess I didn't explain what I was looking for adequately.
With arrows weighing between 350 and 550 grains, (taking F.O.C. into account),
explain the formula and what actual difference that we as bowhunters can see.
Again, I see both as a measurement of penetrating potential, and I also can understand the "mass in motion" theory, but I would like someone that touts the momentum theory over the K.E. theory to explain their stance.

[Texas Grown]

KE is the transfer of energy "from" the moving object "to the other object at impact". Often misused in describing the energy needed with an arrow to get "through" a deer. But it dose help with identifying a "marker" when trying to determine how effective an arrow with a known weight would be at a given speed.

Remember the kinetic balls when you were a kid? 4 or 5 balls each on a string. You raised one ball and let it swing into the next in line. The energy would transfer to the ball on the other end of the line and it would swing out. Then back to transfer the energy back to the one you started with. The balls in the middle never moved. They were desk top pass time items.


Momentum is the stored energy in a moving object. Also known as the product of mass and velocity of an object. It is controlled by the weight of the object and the speed at which it travels. The higher the weight, the more momentum/energy that is needed to make the object move, and retained while moving.

This is why some bullets, like lighter and/or smaller ones, do well on deer sized and smaller game. The energy is transferred at the point of impact (KE) which not only dose less tissue damage, but transfer's shock to the body and central nervous system at the same time. These bullets are most effective with no pass through. That's why you see some drop in their tracks vs. a heavy bullet with a pass through with the animal running a distance before expiring from tissue damage.

I feel to many preach KE in hunting arrows these days. When in fact, it should be "momentum" being preached. It is momentum that will get the arrow through a deer, not KE.

Don't get me wrong. Speed is good. But if the arrow is to light, it looses energy at longer distances, and looses energy faster, which may lead to lack of penetration. With to much weight, an arrow may not make it to the same distance. But the speed will be more consistent from start to end. And should a hit occur, a pass through is more likely.

Which is better?
The key here is finding a happy median between arrow speed and retained momentum. And understanding your archery equipment, and how effective it is at given distances.

[Texas Grown]

Sorry Rocky. you posted before I got finished .

[Skullworks52]

Get hit broadside with a VW and compare that to getting hit broadside with a Semi. You might survive the VW hit even at 70mph. Not likely with a big semi weighing 80K.

Just a thought wouldn't it be better to compare it more accurately? A semi is over 20 times the weight of a beetle. most would differentiate a heavy arrow being 100-200 grains more, correct? maybe an 18 wheeler at 70 then a beetle at a 100mph?

[bm22]

If i am not mistaken a .300 win mag has over 3,400 ft lbs at 100 yards. The fastest arrown out there has less than 100 ft lbs of KE.

A bullet kills by dumping a large amount of energy into a target creating the large non permenant wound channel we have all seen in ballistic gel.

An arrow kills by cutting veins and blood loss and suffocation.
We as archers are only concerned about making our arrow go as deeply as we can and cut as many veins as possible on the arrow path. We care about momentum, not energy transfer.

The reason momentum is not as popular measure as KE is the speed factor. Speed allows bow makers to differinate themselves from there competition. And is an easy selling point that anyone can understand. Momentum is relies more arrow weight than KE.

Amd there is a reason why most people don't worry about momentum is the fact most modern compounds will easily shoot through a whitetail with a light 300 gr arrow. Its not until a large bone or an odd angle is hit that momentum is needed, when that happens most people blame the shot location and not the arrow. There is also the fact that the faster the arrow the more room for error when judging distances.

I used to be concerned with momentum when I shot my recuve, with my compound i picked a middle of the road 410 gr arrow and expect to shoot through anything in texas, I also stay away from energy draining expandables.

[JW]

I see both as a measurement of penetrating potential.
Explain the difference so that I can understand.

Just shoot the **** thing Rock!!!!


Real simple. My X Wife got pass thrus on most whitetails with a 328 grain arrow pushing the almighty KE formula with 38 foot pounds. Rocky Mountain Titanium 85 grain heads and 3L-18 ACC Easton Arrows. And she killed quite a few.

[TxAg]

You probably already know this, but google Ed Ashby's studies. Tons of info

[Javelin]

Momentum is mass x velocity
KE is .5 x mass x velocity squared.

KE over emphasizes velocity when talking about arrows. Momentum basically tells you how easy or how hard it is to stop a moving object thus the better measurement to use

[JW]

You probably already know this, but google Ed Ashby's studies. Tons of info

Piles of it! I use it for bigger critters and try to adhere to it on my trad bow. But on whitetails with a modern compound, well, they just are not that hard to blow thru. It's good info tho and I think all bowhunters should read it.

[Txnrog]

Momentum is mass x velocity
KE is .5 x mass x velocity squared.

KE over emphasizes velocity when talking about arrows. Momentum basically tells you how easy or how hard it is to stop a moving object thus the better measurement to use

^^^^This. Fairly consistent responses - momentum is the better measurement for penetration of an arrow, which is what we care about. It is just much harder to sell because a bigger part of the equation depends on the projectile than the bow. You really start to see the difference when you shoot trad gear.

One thing I will add is down range trajectory may or may not be worse with heavier arrows. So the speed is more accurate because of less drop doesn't always hold up. Most arrows have a very similar aerodynamic profile, and at certain distances, a heavier arrow that starts slower may travel flatter (higher momentum retains speed better thru equal wind resistance) than a lighter faster one that bleeds off energy more quickly. I personally have had setups that shot heavier arrows with less drop at 40+ yards. Not always the case, but depends on the setup.

[Mudslinger]

Rocky, the only thing I can tell you and this is just my experiences and results is that with a heavier arrow and a higher FOC on the heavier arrow, my bow was a lot quieter, and to my style of shooting it was more forgiving and more accurate for me. To anyone else, maybe not. Does it kill any better or out penetrate the lighter arrow i was shooting, who really knows. The statistics and such show that it should, but does it really. It would be hard to really judge mine considering I went 150 grains heavier on my arrow and about 11% more on my FOC and still had 1#KE more than I started and way more momentum. It worked for me and I tout the heavier arrow, but the most important thing in all this is that each bowhunter must have a tuned rig and accessories, a sharp broadhead, confidence in his equipment and his ability to use that equipment and a well placed arrow. Does it really make a difference in any animal in the US, maybe on a big boar hog, but everything else, probably NO. Tuned bow, sharp head and a well placed shot and just about any amount of KE and/or momentum will kill and get a pass thru on most critters over here.

Sure is fun to ribb and tout and boast about what we have with our set up though. And a heck of a lot of fun to tinker with this stuff!