Home Forums Hunting & Shooting Elk Hunting Enough energy for elk?

Exactly.

Momentum degenerates into force when it strikes something. The more the target resists, the more force that is applied. Those that prefer to think in terms of momentum probably believe penetration does all the killing. Cartridges were once compared by how many pine boards they would penetrate.

Energy is the inseparable other value, just a dumb number..... until the rate of transfer is considered. Remember the 22 Hi-Power. It's maker was telling you that this round would dispense it's energy rather quickly. Does that make it a big game round?...... not necessarily!

Energy is the potential to do work, nothing more. Those impressed with energy fiqures need to pay particular attention to how their bullet choice will react to different target densities. The Berger bullet seems to be a good example of how to get correctly applied power out of a big game bullet. They say it works. The "bomb" is a high power energy exchange.. in the right spot.

Momentum is the more dependable model because it's so rudimentary. You want a hole in something... use a solid. You want wider hole.... use an expander or larger caliber and push it a little faster to keep up with the extra force needed. You want an even wider wound channel all the way thru..... use a tougher expander and push even faster.... fast enough to transfer momentum to the tissue.

Energy on the other hand is much more nebulous (to borrow a word from JB) you need to have a plan to make use of that also. The problem run into is that more energy does not always mean more work will be done or that sufficient power levels will be reached. That's what is giving energy it's bad name around the Campfire.

If you shoot a "magnum" for the power (there are other reasons)you need to extract the energy wisely. If you don't you'll get energy wasted beyond the target, energy that never reaches a vital area.... power levels the bullet can't handle, power levels too low due to low tissue density. That's when the naysayers opine that your magnum adds nothing to the equation.

When talking about energy and momentum you can't leave out the target type, density and toughness. It is equally as important as bullet construction. Jeff O said that elk have a little PD in them and it's true. The problem for bullet makers and cartridge designers is to get to that PD with the right energy transfer or power. A varmint bullet won't do it because the reactive force it meets is too great for it's construction.

The Berger is the closest I can think of right now that can get to the big game prairie dog with the power of the varmint hit. Haven't connected with one yet but JB did.

Anyway, I just wanted to defend energy a little more. It is a 100% real value. It does represent the greatest amount of work that can be done. The 300 will do more work than a 06, however, the 06 is capable of equal power in any single event. The 06 has enough energy to complete the task. I think that's what makes this such a tough topic.

The Truth is out there. Ask the right questions.

I never fail to be amazed by posts having "energy" in the title going for 12 pages with posts on hunters rights or freedom or some bore never raise anybody unless "fences" is in the title.

Coyote: Agreed;things do not always go as planned.A bullet that retains some weight and/or penetrates deeply enough can save the day under a wider range of circumstances than something designed to fragment shortly after impact.

Accubond.

What was the question again? :-)

Collisions problems are an important class of problems in physics. Momentum is conserved in all collisions. Kinetic energy is only conserved in elastic collisions.

Many physics students have difficulty solving collision homework problems. One key for helping with these problems is understanding the different types of collisions and which quantities are conserved in each type.

Conservation of Momentum
The law of conservation of momentum states that the total momentum of an isolated system with no external forces will be conserved. The momentum can be transferred from one object to another, but the total momentum can neither increase nor decrease.

Deciding whether momentum is conserved in a collision is easy. Momentum is conserved in all collisions. When doing a physics homework problem involving a collision, the total momentum is always the same before and after the collision. Always use the conservation of momentum equation.

Remember that momentum is a vector. In a two or three dimensional collision problem it is absolutely essential to add the momenta of the different objects according to the rules of vector addition. Divide all momenta in the problem into x and y components (and z for a three dimensional problem). Leaving out this step will virtually guarantee a wrong answer.

Conservation of Kinetic Energy
Energy is one of the fundamental quantities that is always conserved. The total amount of energy in an isolated system can neither increase nor decrease. Energy can however change form. That means that the total amount of kinetic energy in a system can change. Kinetic energy can decrease if it is converted to some other form of energy. If another form of energy is converted to kinetic energy, the total kinetic energy of a system can increase.

Working with kinetic energy equations can in some ways be easier than with momentum equations, but it can also in some ways be more difficult. Energy is a scalar rather than a vector quantity, so there is no need to divide energy into components. However velocity is squared in the kinetic energy formula, so solving kinetic energy equations often requires solving a quadratic equation.

In some collisions the initial kinetic energy can change form. For example if the collision produces a noise, kinetic energy transformed into sound energy. If the collision deforms the objects, some of the kinetic energy goes into deformation. Hence Kinetic energy may not be conserved in a collision.
Types of Collisions
Kinetic energy is conserved in some but not all collisions. Whether the kinetic energy is conserved depends on the type of collision. Physicists classify four types of collisions.

Elastic collisions: Kinetic energy is conserved in elastic, which are also called completely elastic, collisions. To solve these problems, use both momentum and kinetic energy conservation.
Inelastic collisions: Kinetic energy is not conserved in inelastic collisions. To solve these problems use momentum conservation but not kinetic energy conservation.
Completely inelastic collisions: In completely inelastic collisions, the objects stick together after the collision. That means they have the same velocity after the collision. To solve these problems, use momentum conservation and use the same velocity after the collision for the objects. Do not use kinetic energy conservation.
Explosive collisions: In explosive collisions kinetic energy increases. The extra kinetic energy usually comes from stored chemical potential energy. To solve these problems. use momentum conservation only.

Conservation of momentum applies to all collision homework problems. Understanding the different types of collisions helps students know when to use conservation of kinetic energy to solve physics collision problems.[b]

http://mechanical-physics.suite101.com/article.cfm/understanding_physics_collision_problems


[b] A bullet collision is an inelastic collision and therfore no energy is transfered

Jordan �

I�m not sure we have a disagreement. I was discussing two separate incidents, one in which nothing exits the target animal and one in which bullet/bone/tissue do exit.

In the former, all bullet fragments and accelerated body parts come to rest inside the body of the animal. At that point, with zero velocity, kinetic energy is also zero for a loss of 100%.

In the second case, where bullet/bone/tissue exits, the loss of kinetic energy inside the animal is less than 100% but all exiting items eventually come to rest outside the animal. (Unless you are hunting in outer space somewhere.) At that point kinetic energy is also zero.



The case of the bullet fragments and all body parts stopping inside the animal is a series of inelastic collisions. In the case where some items exit, it is again a series of inelastic collisions, this time with air, rain, snow, bushes, trees, dirt, etc. Every item involved in secondary collisions eventually comes to rest, at which point kinetic energy is again zero.

The secondary collisions do not affect the elasticity or inelasticity of the primary collision, so I think we are in agreement.






.

You said that before. Your statement is true enough but the point escapes me. Kinetic energy is not conserved in inelastic collisions but total energy IS conserved. Frankly, an inelastic collision is what I want � one in which some energy goes to deform the bullet and some energy goes to deform the target. If no deformation of the target occurs, no vital systems are disrupted and no death occurs.



That is where you go wrong.
Momentum is conserved in inelastic collisions, as you have stated. Total energy is also conserved. (Do the math.) Kinetic energy is not conserved, nor would I want it to be. If it was, no energy would be available for deformation of the target, which would not be a good thing in my book. I am quite happy that some kinetic energy ends up as heat energy with smaller amounts as sound, electromagnetic and possibly other forms of energy.

http://mechanical-physics.suite101.com/article.cfm/understanding_physics_collision_problems





The above diagram clearly shows that kinetic energy is lost. You can choose to ignore this fact if you wish but, it does not change the fact that it is indeed lost in inelastic collision

How many times do I have to state that I AGREE Kinetic energy is not conserved in an inelastic collision before you can comprehend that I understand that fact??? Maybe if I write it THIS way?

I UNDERSTAND THAT KINETIC ENERGY IS NOT CONSERVED IN AN INELASTIC COLLISION.

Kinetic energy is only one form of energy, however. The Kinetic energy that is not conserved is not really lost � it is merely transformed into other forms of energy. TOTAL ENERGY remains the same, as it must � energy is a conserved entity just as is momentum.

I consider the transformation of Kinetic energy a GOOD THING, as some of the Kinetic energy that is transformed goes to deform the target, disrupting vital systems, ending up as heat, sound and other forms of energy.

You guys need to put down the pocket protectors and step away from your key boards.

If you can manage it, go shooting at some range or p'dog town tomorrow. Put some of that heavy theory into practice.

RH

Agree, it is transformed....+1

TRUE

FALSE
jwp, my friend, you need to look up the definition in physics of the word "conserve." If something is not conserved, it does NOT mean that it is entirely lost, it means that not 100% of it still exists after the collision. Even if the bullet collision system still retains 98% of its kinetic energy between the bullet and the animal bone and tissues combined, it HAS NOT conserved kinetic energy.

A collision has conserved kinetic energy if 100% of the energy before the collision still remains after the collision. 100% before, 100% after.

An inelastic collision means that there is 100% before and LESS THAN 100% after.

TRUE

You are correct "no" is to broad of a statement, to transfer energy thou there must be velocity after the collison and of course there is some even in an inlastic collison most of the time

Well, at least we agree on something�



You are still wrong on this count, however. Although kinetic energy is not conserved in an inelastic collision it does not follow that no kinetic energy can be conserved. In many cases, including bullet impacts, a great deal of kinetic energy is conserved (as in prairie dog body parts being sent in different directions), only to be transformed in subsequent collisions.

In fact, if momentum is transferred to the target, energy is also transferred. The two are inseparable - you cannot have one without the other. If you wish to argue that no energy is transferred to a target in an inelastic collision you must also argue, incorrectly, that no momentum is transferred either.

Exactly When animal hide, tissues, or bone fragments start off at rest before the collision, and are in motion after the collision, they have gained kinetic energy.

Here's a good example:
Berger VLD. Goes inside the animal's rib cage, hits the heart, breaks a hole through the ribs, and stops against the hide. We'll take a piece of the heart as an example. The heart tissue was sitting relatively still before the bullet struck. Afterwards, there were pieces of heart that were put into motion by the bullet. They gained kinetic energy (energy that was transferred from the bullet to the pieces of heart). Later on, they experience other collisions (unrelated to the first collision with the bullet) as the heart chunks hit the ribs cage and stop. Their kinetic energy has now been reduced to zero, BUT, they did indeed gain kinetic energy in the first place from the bullet (there was a transfer from the bullet to the pieces of heart).

There is a lot of imformation on the science of bullet wounds on the Internet, easily accessed by anybody who's interested. This is a lot more informative than the typical arguments we get here about hydrostatic shock waves and foot-pounds. Geez, according to some hunters these days, a bullet has to retain ALL its weight to kill quickly, which exactly the opposite of the truth.

That is exactly what happened to my mule deer this year. 3 shots from a 264 mag. One in the neck to put him out of his misery. All DRT hits if they had been my old Hornady 140s. Lots of those new bullets going on sale soon from my gun safe. 300 WBY 200 gr Nosler Partitions for Elk this year. You can have my share of those penetrators. I want lead and copper spinning every direction after penetration.

jwp475,

I put the word pressure in bold type. The Momentum model does predict direct applied force. It does explain momentum transferred and most of wound channel. But.... it is not useful to understand hydraulic pressure and is not the whole picture.

Pressure is stored energy. And it makes sense that you included it cause energy and momentum are inseparable! They are just different mathematical models that collectively give a remote view of what's happening.

I was going to type more but Jordan and Coyote already did such an excellent job articulating my points.

Great googley moogley!

I would really love to elk hunt some day. Looking forward to trying it.... but I'll be damned if I'll retake the Ph.D. qualifying exams to do it! I'll just take my 30-06 and not worry about it. :p

Will

Will, but does your 30-06 have enough energy for elk...?

Grin...