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Momentum vs Kinetic Energy visualized, no mention of lethality

Discussion in 'General Gun Discussions' started by mcb, Nov 22, 2019.

  1. mcb

    mcb Member

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    I agree with both of your examples. They are good examples of why Kinetic Energy alone is insufficient to predict terminal performance. That said your above statement is wrong, kinetic energy is the only energy source the bullet has to cause bullet expansion and hydroshock and any thing else it does. How much of or how effective it is, is still unknown but if anything happens it was due to kinetic energy being converted to work in the form of bullet expansion and/or hydrodynamic shock damaged to target materials.
     
    Last edited: Nov 28, 2019
  2. Kleanbore

    Kleanbore Moderator Staff Member

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    Absolutely not:

    The deformation and/or expansion of a bullet involves work, which results from the application of energy. Period.

    [There can be no such thing as anAnother identically constructed (as compared to a 150 grain .30 caliber bullet ) .30 caliber, (hypothetically)15,000 gr. bullet. The idea is ludicrous.

    What you have done is to point out that there is more to expansion than energy.

    Materials shapes, and construction play a role. They influence and control expansion

    But the expansion results from the expenditure of energy, That's very basic Newtonian physics.

    Everything else in your post is right on point.
     
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  3. 35 Whelen

    35 Whelen Member

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    I promised myself I would let this go, but then I thought maybe, just maybe they really don't understand.

    The "ludicrous" idea isn't ludicrous at all. Let me try it this way-

    Bob's Bullets specializes in ordinary cup and core bullets. All of his bullets have jackets of identical thicknesses, the cores all have identical alloy composition, and the nose profiles are identical. In other words, the bullets are in every way identical except in length and weight.

    So I decide to load Bob's .30 caliber bullets in my 30-06 as follows-

    A 100 gr. @ 3000 fps
    A 120 gr. @ 2739 fps
    A 150 gr. @ 2450 fps
    A 200 gr. @ 2122 fps

    What these bullet at their respective velocities all have in common is 2000 ft. lbs. of energy. So according to the mantra that energy determines bullet expansion, these bullets, even with their wide variations in velocity, would expand identically; i.e. the 100 gr. bullet striking @ 3000 fps would expand in an identical fashion as the 200 gr. striking almost 900 fps slower.

    Nope.

    35W
     
  4. Kleanbore

    Kleanbore Moderator Staff Member

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    NO!

    No one has said that energy determines bullet expansion.

    The point is that the expenditure and conversion of energy is what causes expansion.
     
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  5. david58

    david58 Member

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    Precisely. Physics is not simple, but this is simply physics.

    Very clearly the different bullet weights cited would have resulted in different shape/volume. Length and weight differing will determine the differences in expansion. The energy imparted will make the expansion happen, within the limits defined by the bullet design. Gotta have the energy to make it happen (or they'd expand sitting on your shelf), but the design is the basic determination.

    If you took a bullet of a selected design, and varied energy, you'd find that the expansion/penetration would differ based on energy. The design (length, weight, etc) will be the property that defines that curve, varying with the different energies.

    Combining the factors of expansion properties with energy you get to observe the damage done to the target.
     
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  6. Tom-R2

    Tom-R2 Member

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    Although numerous tests using different calibers, penetrating to the same distance in gel is being used as trying to say that all of the current self defense rounds perform (somewhat) equally, I'm not convinced. A 124 grain 9mm @ 1000FPS may travel and expand to a similar depth and diameter as a 124/125 grain 357SIG @ 1400FPS but there is a difference in the momentum and energy of those two rounds, and it's being absorbed by the target. It has to have SOME effect, although it may not be incapacitating. Physics says there is some effect. If we are talking about a living piece of tissue, certainly it matters what tissues are absorbing that energy. Caliber, mass, velocity, projectile type and design, specific tissue of the target, depth of penetration, energy absorbed, and damage caused, added to the psychological reaction to the injury all enter into the results. The higher levels relating to the projectile, and more sensitive the target, the more serious the results are likely to be. But it's still left to fate to a certain extent, there are people walking around in the world who have had a bullet blast through their brains and they are still here.
     
  7. tipoc

    tipoc Member

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    We measure kinetic energy in a specific way. It's in foot pounds. It is a measure of the ability to perform work. So one ft pd is the amount of energy that it takes to lift a one pound weight one foot off the ground. 300 ft pds. is the amount of energy needed to lift that one pound weight 300 ft. off the ground, or a 300 pound weight one foot off the ground, same thing from the point of view of kinetic energy.

    So it's a measure of the ability to perform work. Bullets do work. They lose some energy traveling through the barrel. They lose some to heat and noise. They use some in bucking the wind and in rotation. They lose a great deal in penetration and expansion once they strike. So energy is one of the critical factors to be looked at in ammo selection for a particular job.

    When we read about a 124 gr. bullet moving at 1200 fps the bullet weight is a stand in for momentum and the velocity a stand in for energy, both together that is. Both those figures tell us something. Lacking though, to get a better idea is the type of bullet and it's construction. A JHP bullet suggests a self defense load with the edge to expansion while a hard cast lead swc suggests an edge for penetration with limited expansion where the latter isn't critical to the outcome (same with ball ammo).
    None of these and other criteria will tell you how the bullet will perform when it strikes a target. But they will help provide the shooter with an edge in selecting the right bullet for the specific job. By doing that you increase the potential for a successful hunt.

    That's why the figures for energy are important.

    Heavier bullets retain their energy over longer distances and thus their potential lethality.
     
  8. Double Naught Spy

    Double Naught Spy Sus Venator

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    Which is really what everybody wants to be able to know.

    Incomplete information MAY provide the shooter with an edge in selecting the right bullet for the specific job. Properly understanding that the information is incomplete is a failure on the part of consumers that the ammo manufacturers have made bank on for decades.
     
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  9. BAMASUPER45

    BAMASUPER45 Member

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    Hey, your graph hurts my head, this early in the morning(ha). The other day I watched video of LehighXtremeDefense 65 gr (17XXFps) and it did penetrate Level IIIa body armor, but after the penetration, the bullet went about 5-6" in the gel pack. My nephew (2 tours in Iraq) told me to get the Lehigh 120gr (1600fps) Xtreme Defender, if I wanted penetration. I chose the Xtreme Penetrator 45 Super 200 gr (1100fps)($45 20rns), because I believe that it will penetrate pretty well, and still penetrate enough for SD. I currently use the Buff. Bore 45 Super 255 gr. hard cast , I've had to ream my "leade" to get the bullet to seat right, not to mention xtra power mag springs, and a couple other changes.(G21G4). Yes, I believe in penetration. It ALWAYS gets me, when I see shooters on the internet, shooting through denim-gel packs-28 ga. metal and yelling "WOW". This isn't the OK Coral where we meet in the middle of the street, at high noon. I believe that most people will be behind cover(car fender, corner of house/wall,tree/bushes). AND, you see those guys in Alaska toting large caliber pistol/rifles(and the guide has slug shotgun hung over his shoulder). I know there are stories where the guy killed a 700-800 lb grizzly, with a .22, or a 500 lb boar with a .38.
    I'm not saying my choice of the Lehigh Xtreme Penetrator 200 gr., will be the "ALL" bullet, but I would feel better knowing it would take a heck-of-a-barrier to stop this bullet(1100fps). I did a test with my brother's .357 Mag, (125gr.,hard cast-hot loaded) with my 255 gr hard cast 45 Super, and I was impressed with the .357, BUT when I looked at the barrier's (metal and water jugs), the .357 busted the same amount of jugs, but when I held the the .357 jugs, they flopped in my hands, and when I looked at the 45 Super jugs, they didn't flop much at all, because it stretched the jugs so much, they were stiff.
    Some people say "small and fast", some people say "big and slow". Me, I like "BIG and FAST". I ordered 2 boxes of the Lehigh XP 200 gr., and I will see how they test against my Buff. Bore 45 Super Hard Cast 255gr. I believe the Lehigh will be close, maybe out perform the Buff Bore. Oh yeah, the Lehigh XD 65 gr. that penetrated the Level 3a body armor, was shot out of a M&P 5(12"brl), doing right at 2000fps. Just my .02.
     
  10. d2wing

    d2wing Member

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    The measurement of momentum has no application on soft tissue. It is a measurement of movement. Living tissue is not like a solid except for parts like bones. Flesh acts more like a liquid. As velocity goes up , resistance to displacement goes up like a boat in water. As velocity goes up the inability of fluids to compress comes into play as well as the rate tissue can separate or be displaced. This is what causes the wound channel to expand perpendicular to the axis of the wound channel. The higher the velocity the wider the wound energy is displaced. This is why a high velocity bullet does more damage than a slower bullet of the same energy or mass depending on other factors like construction. This is also why in some circumstances a slow bullet will penetrate deeper than a faster bullet. Less resistance and less expansion. Expansion is resistance of the flesh working on the bullet causing damage and releasing energy of the bullet. Also why heavy solid bullets work on very large game. The measurement of momentum has no application in wounding or the work a bullet does. If you shot a steel plate and the bullet was stopped by the plate, you could measure the movement of the plate to determine momentum less the energy to deform the plate I guess. To measure momentum as a factor in wounding is a useless exercise to entertain folks on gun forums. But I am very sure it won't stop any of you. Have fun with your endless futile attempts to make momentum a useful measurement for bullets as it can never be valid or scientific.
     
  11. d2wing

    d2wing Member

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    You are discussing things without any basic understanding of how bullets work or the meaning of the terms you use. I have tried to make it simple for you. I hope my explanation helps.
     
  12. mcb

    mcb Member

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    Momentum has every bit as big of a role to play as kinetic energy does in biological target interaction. Conservation of momentum is as valid and true in liquid and gas systems as it is in solid mechanics it's just harder to do the math in those mediums. You must conserve energy and (total energy not kinetic energy) momentum.
     
  13. d2wing

    d2wing Member

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    I am a big fan of the M2 Ma Deuce. High velocity .50 cal. Bigger and faster is better.
     
  14. d2wing

    d2wing Member

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    Clearly you don't know that you are talking about two very different things. The measurement of momentum is a measurement of velocity, kinetic energy is a measurement of work. You can't mix them together. You should stop.
     
  15. mcb

    mcb Member

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    A object that has Momentum also has Kinetic Energy you can't have one and not the other that is a physical impossibility for and object with mass. The two properties of momentum and kinetic energy are inseparable properties of mass in motion. This is something you learn in highschool physics.
     
  16. d2wing

    d2wing Member

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    They are separate measurements. That's like saying volume is the same measurement as weight. They are two separate measurements and they measure different things. I have already explained that. You must have slept in class.
     
  17. mcb

    mcb Member

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    Seperate properties that are inseparably related for objects in motion. If you can calculate one you have all the information to calculate the other. If one changes so does the other one. Other than the simplest of collision models you need to use both values along with a bunch of other information to come to a meaningful solution to the model.
     
  18. d2wing

    d2wing Member

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    I suppose you could say that a bullet arrived with a certain amount of momentum, as that bullet passed through flesh, momentum is converted to kinetic energy until all the momentum is converted to kinetic energy or the remaining bullet exits slower with less mass having lost momentum. But that doesn't account for the amount of energy because Kinetic energy is not a measurement of momentum and they are not equal. To do that you would have to convert the measurements to Kinetic energy both before and after and subtract the difference being the energy used. Pointless. Only kinetic energy did the work.
     
  19. mcb

    mcb Member

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    Not sure how to unpack that. First you say they seperate measurements not related then you say you can convert one to the other.
     
  20. d2wing

    d2wing Member

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    The point being that momentum can be converted to energy but the values will change by V square at each point, and it is kinetic energy that does the work not momentum. Momentum is not a measurement of work so is a useless measurement in ballistics.
     
  21. Jim Watson

    Jim Watson Member

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    Momentum and energy are both conserved, q.v. Newton.
    But there are many forms of energy. Heat and broken bonds by energy.
    But momentum is mv full stop. When it appears that everything has stopped moving, the momentum has been transferred to the planet.
     
  22. d2wing

    d2wing Member

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    You can convert momentum to energy by using the same variables. They are not equal to each other. But the values will change in a nonlinear way. And kinetic energy is the measurement of work. Momentum doesn't do work. There is no point in measuring momentum. A moving object has momentum the tendency to stay in motion unless acted on by outside force. And it has potential kinetic energy the potential to do work. they are not equal and not measured the same but use the same variables. If a solid abject hits another the momentum is transferred to the other object resulting in a vector of movement of that object. However some of that momentum is converted to energy , friction, heat, fluid movement, deformation etc. Both energy and momentum are used buy they are measured differently. If the second object is moving from being hit that object has received transferred momentum. Parts damaged have used up energy. That's kinetic energy. The measurement of momentum is not a concern in ballistics. The work or energy is. You are not trying to move objects, you are trying to destroy them.
     
    Last edited: Nov 30, 2019
  23. mcb

    mcb Member

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    There is no converting they are simply interdependent properties. That was the whole point of the graph in the first post. It shows the relationship between kinetic energy and momentum as we change mass and/or velocity of a projectile.
     
  24. d2wing

    d2wing Member

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    Momentum is a measurement of an object to remain it motion, that's it. I accept that it is a way of explaining penetration, although not really correct it is easier. Because peoples eyes glass over if I talk about resistance increasing by velocity and deformation.
     
    Last edited: Nov 30, 2019
  25. d2wing

    d2wing Member

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    Ok. Merry Christmas.
     
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