Poll of the Day > Guns question (sciency)

(+) Yeah! (+)

is the damage of a bullet/shell against a hard target (metal/cement/concrete) based solely on the Force (Newton-Meters/Foot-pounds) or does the size/mass affect the damage separately?

I asked on r/askscience but they're hella slow...

Basically, if you just mortar a 50lb shell at a wall or fire a hyper-sonic grain of tungsten/lead at that same wall so they both impact with the same Force (say.... 5000 Newtons), will they do similar damage?

This is against a hard target only since the damage to a gooey person would be wildly different.

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mass and density would likely be variables, but im only a lover and an actor, ok?

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ClarkDuke posted...

but im only a lover and an actor, ok?

you're probably very huggable

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Lokarin posted...

you're probably very huggable

you better believe it, ok?

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I think it's kinetic energy E = mv/2 (joules, kilograms, and meters per second)

so, the energy increases with mass linearly, but with the square of the velocity

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Sahuagin posted...

I think it's kinetic energy E = mv/2

so, the energy increases with mass linearly, but with the square of the velocity

Ya, I'm asking if the damage would be the same if the end "E" was the same

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Lokarin posted...

Ya, I'm asking if the damage would be the same if the end "E" was the same

I think theoretically, yes... but you can't really change the mass independently without changing other properties of the projectile, so I don't think it would be able to literally be identical. (ie, if the mass increased, then either the size or density of the projectile increased, and if the density increased, then probably so did the hardness.)

also, different masses and velocities would be affected by drag differently as well.

the best way to know this for sure is to set up a test and fire your projectiles and compare the differences. (see Paul Harrell for exactly those kinds of demonstrations: https://www.youtube.com/channel/UC6QH13V2o68zynSa0hZy9uQ )

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Lokarin posted...

Basically, if you just mortar a 50lb shell at a wall or fire a hyper-sonic grain of tungsten/lead at that same wall so they both impact with the same Force (say.... 5000 Newtons), will they do similar damage?

How could they? The surface area is completely different. You're talking about two very different types of damage. A 50 lb shell will likely knock a good portion of the wall down (even if it doesn't actually penetrate) whereas a super-sonic grain of whatever will simply create a small hole (well, probably more than that -- a science guy would be able to estimate the damage better).


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Ya, I just meant "mostly" the same - they don't have to be identical, only similar levels of damage. There's something in armour called "overmatching" when a projectile is larger than the thickness of the armour where it has different properties because the energy required for a ricochet is transferred passed the armour so the energy is kinda re-applied (like an elastic that springs back)

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Zeus posted...

How could they? The surface area is completely different. You're talking about two very different types of damage. A 50 lb shell will likely knock a good portion of the wall down (even if it doesn't actually penetrate) whereas a super-sonic grain of whatever will simply create a small hole (well, probably more than that -- a science guy would be able to estimate the damage better).

Yes, that's literally the question at hand.

If you throw a bowling ball at someone, ouch - but if you golf a golfball at someone that's gunna cause some rage face! Energy might be more important than size.

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Lokarin posted...

If you throw a bowling ball at someone, ouch - but if you golf a golfball at someone that's gunna cause some rage face!

there's something about comparing masses/densities of projectile vs target but I'm not sure of the details. a small fragile projectile hitting a hard surface will have its energy reflected back at it. a small hard projectile hitting a soft surface will tear through it. a large massive hard projectile hitting a medium soft/fragile target will destroy the target (at sufficient speed).

I think the question is where the energy is transferred. I think it is transferred into the weaker (less dense) object (damage is applied to the weaker object), but not sure of the details.

reading about it, this is inelastic collisions, but I've never taken physics and am pretty novice at this subject. you have to take into account the masses and velocities of both objects, and then use conservation of momentum or something. I'm not sure if density or penetration fits with that though. (maybe penetration is an elastic collision?)

some really good info on this (physics of gunshots) here: https://www.futurelearn.com/info/courses/maths-linear-quadratic/0/steps/12123

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The word you're looking for is pressure, or force per unit area. An equal force applied to a smaller area will be more capable of piercing through the target, because the material being hit can only withstand so much pressure before physically being split through instead of simply being compressed.

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