Physics question (About Guns)

ollopa said:
To be pedantic, Newton's third law refers to force, not momentum. In a collision of two objects, there will be an equal and opposite force applied to each object. If they have different masses, then the resulting acceleration of each object will be different. Remember that force involves mass and acceleration whereas momentum involve mass and velocity. Conservation of momentum can be derived from Newton's third law, but "equal and opposite" is not talking about momentum.
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True, but I didn't mention Newton's third law, and was referring specifically to the ballistics case where the bullet and gun (i.e. two rigid bodies) are pushed apart by an exploding charge. In this case, since the total momentum (a vector quantity) must remain zero, the two bodies will have "equal and opposite" momentum.
 
Was dope legalized in Texas?

SixPapaCharlie said:
Einstein taught us that for every action there is an equal and opposite reaction.

So when I fire a gun, the gun hits me with the same amount of force that the bullet has. True?

It would seem that the bullet has more energy but that wouldn't be possible. As Alexander Graham Bell taught, the amount of energy in a system is fixed. It can not be created nor destroyed, it can only change forms. I believe that is the 3rd law of turbo dianetics.

Anyway is it true to say I am being hit with the same force as my victim?

Actually I would be getting harder because my victim will have been hit by a bullet that has lost some energy due to the law of diminishing returns illustrated on the Kinsey scale.

Now the gun hitting me is applying the same amount of force but distributed over a larger surface area so I end up intact, Just a little bruised.

If the back of a gun were filed into a point the size of a bullet, when I fired it, the gun then should have the same (or even worse) effect on me than the recipient of my bullet.

I feel like some energy is missing somewhere. The bullet seems to be doing orders of magnitude more damage than a gun and the surface area difference doesn't seem large enough that the difference in damage on both sides of the equation would be so different.


And by the way, I was just kidding. I know it wasn't Einstein. It was Thomas Edison.
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azure said:
RotorDude is correct and gave the most correct explanation. Another way to say it: we're more familiar with kinetic energy in the form (1/2)mv^2, but it can also be written as (p^2)/2m where p is momentum. Bullet and gun have the same (and opposite) momentum, but the bullet, having much less mass, has much more kinetic energy and therefore way more potential to do damage.
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Interesting discussion, wiki gives a pretty good rundown of recoil and the causes. https://en.wikipedia.org/wiki/Recoil
 
I checked this week, and my 30 round magazines for the AR and AK all self-identify as 10 rounders, and the AR and AK self-identify as single shot bolt-action rifles, so it's all good.

Love this self-actualization stuff.
 
I never got too concerned about the physics. All I really care about is that the 180 grain projectile does it's intended job at the end of it's flight. Recoil ain't no big fat hairy deal unless you're shooting a cannon.
 
Yeah, Not momentum, not energy. Force is what Newton is taking about. F=m*a . bullet is light, so it accelerates a lot to high speed. gun is heavy, so it accelerates a little to low speed(dampened by reload action even more if automatic). Nothing about momentums or energy in Newton'w 3rd law.
 
genna said:
Yeah, Not momentum, not energy. Force is what Newton is taking about. F=m*a . bullet is light, so it accelerates a lot to high speed. gun is heavy, so it accelerates a little to low speed(dampened by reload action even more if automatic). Nothing about momentums or energy in Newton'w 3rd law.
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This. When a gun is fired m×a(bullet) = m×a(gun)

So, as mass increases, acceleration decreases. This is the exact reason big heavy cars/trucks are safer in collisions. As mass increases to infinity acceleration approaches zero.
 
Mtns2Skies said:
This. When a gun is fired m×a(bullet) = m×a(gun)

So, as mass increases, acceleration decreases. This is the exact reason big heavy cars/trucks are safer in collisions. As mass increases to infinity acceleration approaches zero.
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Oh....don't tell the Prius owners that. :)
 
Mtns2Skies said:
This. When a gun is fired m×a(bullet) = m×a(gun)

So, as mass increases, acceleration decreases. This is the exact reason big heavy cars/trucks are safer in collisions. As mass increases to infinity acceleration approaches zero.
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This is also correct, and I'm not sure why you think it contradicts what I or anyone else wrote. Newton's second law can also be written in terms of momentum: F = dp/dt. The equal and opposite forces, acting over the same time interval, impart equal and opposite momenta. Also, because p = m*v, the bullet, having much smaller mass, has much higher velocity.

For some purposes it's more convenient to work with force, for others it's more convenient to work with momentum. For collisions and explosions with a clearly defined "before" and "after", it's usually more convenient to work with momentum because the force is not constant during the interaction. But the two ways of looking at the problem are entirely equivalent.
 
azure said:
This is also correct, and I'm not sure why you think it contradicts what I or anyone else wrote.
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Why do you think I think it contradicts? Quite contrary I was agreeing ?????
 
Mtns2Skies said:
Why do you think I think it contradicts? Quite contrary I was agreeing ?????
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Well, the poster you were supporting with a "this" (genna) evidently thought what he wrote contradicted what I and others wrote. I probably should have quoted his post rather than yours, but yours had the math and his didn't. Sorry if I misunderstood your position.
 
azure said:
Well, the poster you were supporting with a "this" (genna) evidently thought what he wrote contradicted what I and others wrote. I probably should have quoted his post rather than yours, but yours had the math and his didn't. Sorry if I misunderstood your position.
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I reread his post and see that I misread his first line. My bad.:oops:

Just different ways to represent the same thing.
 
A 98 pound 155mm artillery round will rock the 27 ton SP howitzer pretty good. Fortunately, the hydraulic recoil system absorbs that energy and returns the gun to battery in just a couple of seconds.
 
N3368K said:
A 98 pound 155mm artillery round will rock the 27 ton SP howitzer pretty good. Fortunately, the hydraulic recoil system absorbs that energy and returns the gun to battery in just a couple of seconds.
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That looks like Charge "Super 8" in action from the dust kicked up by the concussive force and the full recoil stroke...though the towed howitzer is a great deal lighter than a self-propelled (SP) howitzer so it rocks even more!!! Great stuff.

I spent over 20 years doing this...and fired over 100,000 rounds, though mostly 105mm in light units vs heavy. Big guns were fun. :D
 
To understand this best---- find a Remington 600 saddle gun chambered in 350 Remington mag, shoulder it and squeeze off a round.


You'll know :)

It'll kill over there, and wound over here.
 
I spend many days with either a 45-70 Guide Gun or a 500 Magnum pistol. They make me smile. Neither is particularly light. My ultralight mountain rifle is less potent and more punishing to shoot. I never feel the kick when hunting, only on the range.
 
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N3368K said:
That looks like Charge "Super 8" in action from the dust kicked up by the concussive force and the full recoil stroke...though the towed howitzer is a great deal lighter than a self-propelled (SP) howitzer so it rocks even more!!! Great stuff.

I spent over 20 years doing this...and fired over 100,000 rounds, though mostly 105mm in light units vs heavy. Big guns were fun. :D
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So when the gun relocates itself several feet like that do you have to recalculate your fire solution, or will it not matter all that much?
 
wanttaja said:
As Dennis pointed out, this is WAY not true. Are you familiar with the term "loose cannon"? Old nautical term referring to what would happen if the breeching ropes failed when the gun fired. Ordinarily, the cannon (usually) didn't destroy anything because the recoil was expected and planned for.

Historical reports indicate that the recoil would sometimes make the guns jump clear of the deck...not bad, for a ton and a half of iron. And yes, sailors were mangled and killed from not getting out of the way.

The recoil was useful, as it threw the gun back inboard and made it easier to swab out and reload. But running that mass of iron out after reloading took work, you might have eight or a dozen sailors on the training tackle.

Some guns had fixed carriages (carronades) but the gun itself would be set atop a sliding element, typically greased with the fatty residue produced when the salt beef was boiled (known as "slush"). However, the carrronades were less efficient; shorter barrels, much bigger calibers. The intent was to fire a big, heavy cannonball slowly, on the believe it would create more damage.

Ron Wanttaja
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To amplify Ron's correct response above, on Iowa-class battleships the entire 58,000 ton MGW ship would move six to eight feet sideways when a full broadside was fired. You can see the wake made by the bow in this photo. 9 2000lb shells launched on a 20+ mile journey:
 

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Bryan, if you're enjoying "shotgun shoulder," you're going to love "scope eye."
 
vontresc said:
So when the gun relocates itself several feet like that do you have to recalculate your fire solution, or will it not matter all that much?
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The gun returns to battery very closely due to the recoil mechanism but the "sights" are checked against the aiming point between rounds, typically to ensure everything is still on the right data. The aiming point is a collimator sight (most accurate), aiming posts (two posts aligned near and far) or a distant point.

If speed is more important than accuracy, we would sometimes fire 3-5 rounds between checking sights on 105mm.
 
Tom-D said:
To understand this best---- find a Remington 600 saddle gun chambered in 350 Remington mag, shoulder it and squeeze off a round.


You'll know :)

It'll kill over there, and wound over here.
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A Remington 600 in 6 mm Remington is bad enough. I don't even want to think about shooting one in .350 Rem Mag.
 
All right ballistic gurus, here's a question for you.

You shoot an arrow. You will notice that the arrow takes an arcing trajectory and generally points in the direction of travel.

Will a bullet point in the direction of travel as it's trajectory arcs?
 
Didn't they teach you that **** in the army????
 
Sac Arrow said:
All right ballistic gurus, here's a question for you.

You shoot an arrow. You will notice that the arrow takes an arcing trajectory and generally points in the direction of travel.

Will a bullet point in the direction of travel as it's trajectory arcs?
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yes, if it's buckshot.

EDIT: sorry, I forgot the " :) " for those that couldn't pick up on my moderate dose of humorous sarcasm.
 
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Not really due to spin. The nose will be slightly offset to the line of flight. Also, due to Coriolis effect, it isn't really tracking straight over the ground either. Do you want to talk about the effects of wind, humidity and temperature as well? Afterwards, we can discuss internal ballistics too. The effects of temperature on powder burn rate, barrel droop and jump, etc. :D
 
Coriolis doesn't always affect the bullet's travel. There are some YouTube videos that are way off in trying to explain it.
 
I was being somewhat facetious implying some artillery factors such as Coriolis effect. I'm not a long range rifle shooter. :D
 
I do know the answer to the question. I was curious to see what kind of responses would pop out. Rotordude's link explains it well.
 
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