Kenetic Energy

[Eck]

Duck Hunt's testing is consistent with my experiences with 16" bolts in my Micro compared to 20" bolts out of my ExoMag.

Don't discount the short, light bolts until you've shot them a bit.

As for the KE argument, crunching the numbers on my bow/bolt combination, the difference is 1 foot-lb at shooting distances - not worth arguing about. With a pass-through, any KE carried by the arrow is wasted energy anyway.

Archers kill by hemorrhage, not KE.

[Species8472]

Archers kill by hemorrhage, not KE.

Agreed, however added KE and especially momentum can make for a more forgiving setup.

Case in point, two years ago i took a mature buck and as the bolt left the crossbow one of the three vanes detached resulting in a hit that was high and right and square on the shoulder blade.

I was shooting a 405 loaded with 500 grain zombie slayers tipped with 125 grain hair splitting sharp fixed heads. The shot destroyed both shoulders and anchored the deer on the spot. I am pretty sure a lot of other lower momentum combos would have resulted in a lost deer.

[DuckHunt]

My Executioners, 18 or 20 inch, will have a lower poi than my zombies, 18 or 20 inches. All of these are fletched with 2" blazers.

Hmm. Assuming the same components are used, the Executioners would be a touch lighter (.1gr/inch). Thats interesting that the Zombies hit higher. Spine could indeed be the difference.
DuckHunt

[Czy_Horse]

I feel KE numbers are only valuable if you understand what the number really is .
It is a value that is given to an object in motion .

I agree because the KE formula does not use any of the objects physical dimensions in the calculations only the mass of the object and speed of the object.

Archers kill by hemorrhage, not KE.

In my left hand I'm holding a 400 grain maxi-ball . . in the right I'm holding a 400 grain arrow c/w sticky sharp broad head. Both will have the same potential energy at rest and the same KE (energy in motion) as soon as released. *Now hold out your hands . . which one do you want me to drop?

Czy_Horse

*Don't try this at home!

[nchunterkw]

We have these threads all the time with the same basic arguments....or I mean discussions. If you really want to understand arrow penetration, read this.

http://www.tuffhead.com/ashby_pdfs/ashb ... ration.pdf

[galamb]

At 30 yards my 243 Winchester shooting an 80 grain mono-metal bullet has an impact energy (KE) of about 1900 foot pounds.

At 30 yards my Vixen II shooting my 394 grain arrow has an impact energy (KE) of about 56 foot pounds.

The bullet from the 243 will NOT penetrate to the other side of a 6" thick sandbag full of sand.

The bolt from the Vix II WILL penetrate to the other side of a 6" thick sandbag full of sand.

KE is but one measure that is tossed around as the "grail" when trying to determine whether something is lethal or not - it's something article writers could use - it's a simple number that gives a quick and easy way to compare Apple A to Apple B, but beyond that it's really of little value (unless you are comparing apples).

While I do agree it is "useful" in a total comparison, once you start talking about arrows "of whatever length" you also have to consider momentum and slug force - and when talking about bullets you also need to consider hydro-static shock and wound channels.

For if you don't, and in my example above you instead used "penetration through sand" as a "lethality" measurement (call it PTS so that you have a neat term to write about), you would conclude that a 243 is "ineffective" @ 30 yards, possibly incapable of taking down a deer, where the Vixen II is "far superior" since the arrow would penetrate through the vitals "much better".

[Eck]

OK, we have some folks misunderstanding and mixing aspects of physics here.

At the risk of offending some by coming off as your High School Physics Teacher, kinetic energy is a function ONLY of mass and velocity. Shape, size, aerodynamics do not enter into the equation. LITERALLY. 100 foot-lbs of force is 100 foot-lbs, whether the projectile is a bullet, feather, or a barn door.

Ballistic efficiency, parasitic drag, etc. are separate factors that will cause less efficient objects to bleed speed, therefore energy, faster. That results in a loss of kinetic energy. 2 objects of the same mass can start at the same velocity, the one that looses velocity faster loses energy faster.

While I'm at it, "momentum" is the same thing as "Kinetic Energy". Kinetic energy is the energy of motion.

[Species8472]

OK, we have some folks misunderstanding and mixing aspects of physics here.


While I'm at it, "momentum" is the same thing as "Kinetic Energy". Kinetic energy is the energy of motion.

Not to further the misunderstanding going on but KE and momentum, while related, are not the same thing. Mathematically momentum is the calculus derivative of KE or inversely KE is the integral of momentum. Momentum is the product of mass times velocity and KE is 1/2 mass times velocity squared. All else being equal if you have two bolts with the same KE the heavier one will always have a higher momentum and a greater ability to penetrate (that's why heavy bolts are used for large heavy boned animals).

[Eck]

OK, we have some folks misunderstanding and mixing aspects of physics here.


While I'm at it, "momentum" is the same thing as "Kinetic Energy". Kinetic energy is the energy of motion.

Not to further the misunderstanding going on but KE and momentum, while related, are not the same thing. Mathematically momentum is the calculus derivative of KE or inversely KE is the integral of momentum. Momentum is the product of mass times velocity and KE is 1/2 mass times velocity squared. All else being equal if you have two bolts with the same KE the heavier one will always have a higher momentum and a greater ability to penetrate (that's why heavy bolts are used for large heavy boned animals).

Point taken; your definition is correct. The difference between the two is only really manifested however in the situation where one or both bodies cease motion as a result of the collision. This is not true in a "pass through" as we typically experience with arrows. The only object impacted by the momentum is what stops the arrow.

[bitemybait]

FYI
To find out KINETIC ENERGY
Formula is = arrow weight x velocity x velocity divided by 450,240
= true kinetic energy
Then there is no guessing

[nchunterkw]

OK, we have some folks misunderstanding and mixing aspects of physics here.


While I'm at it, "momentum" is the same thing as "Kinetic Energy". Kinetic energy is the energy of motion.

Not to further the misunderstanding going on but KE and momentum, while related, are not the same thing. Mathematically momentum is the calculus derivative of KE or inversely KE is the integral of momentum. Momentum is the product of mass times velocity and KE is 1/2 mass times velocity squared. All else being equal if you have two bolts with the same KE the heavier one will always have a higher momentum and a greater ability to penetrate (that's why heavy bolts are used for large heavy boned animals).

Point taken; your definition is correct. The difference between the two is only really manifested however in the situation where one or both bodies cease motion as a result of the collision. This is not true in a "pass through" as we typically experience with arrows. The only object impacted by the momentum is what stops the arrow.

I have no idea what you are trying to say....

Momentum is the tendency of an object in motion to stay in motion. When two similar object strike the same thing, the one deriving most of it's momentum from the mass of the object will stay in motion longer that the one deriving most of it's momentum from the velocity. This is because the resistance forces the objects encounter vary with the square of the velocity so the lighter faster object encounters higher resistance forces than the heavier slower object does.

Please, take a look at the document I referenced......it will clear up a lot of things....

[Hi5]

Shorter arrows paradox is less than the longer arrows. They regain their trajecty arc faster

I'd say that the reason the shorter arrows hit higher is because they flex differently. All other things being equal, the shorter arrow flexes less. (Vixenmaster just says it better.)