How is it that a bullet that is 12.7 mm in diameter can kill somebody with so much more bodily damage than a 20mm rebar rod that is impaled through the body? I see stories of people surviving impalement all the time, but a shot with a .50 cal to the same area almost always results in instant death. Shouldnt the bullet just go through its target because it travels so fast?
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A 12mm bullet traveling at a high speed makes a bigger hole than a 20mm rebar when a body is traveling at a few meters per second. Rebar also doesn’t distort as it tears through a body.
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The rebar isn’t moving at 2,910 feet per second, for starters. Nor is it spinning at a rate of one turn every 38 inches (that’s roughly 55,000 rpm). It isn’t the size of the hole, it’s the amount of kinetic energy imparted which results in severe hydrostatic shock.
Edit: added the rpm for the rotation.
The bullet strikes your flesh. Your flash has to move out of the way, and very very fast. It gets blasted out of the way. A wave of pressure flies outward violently, moving and smashing your insides as it goes. This wave is concentrated towards the exit wound, bursting out the back and creating a hole significantly more gruesome than the entry.
A stabbing can have its own issues, but really won’t destroy much outside of its path.
Things that impact at high speeds exert energy onto objects they impact.
As an example.. an asteroid that impacts makes a crater… a bullet hitting a sheet of metal does a similar crater.
Well.. the sheet of metal and the floor generally are solid enough that the energy can only crater like this.. in the case of a human body however…well that energy doesn’t “bounce back” like on a bulletproof vest or a sheet of metal.. it carries through ripping a bigger exit wound than the entry wound.
In addition a bullet hitting an object will change its trajectory, maybe explode, break apart and whatnot.. that causes damage too “overpenetrations” like you expect can and will happen.. practical examples..a tank hitting a wooden building.. that shell won’t explode….but they still make Exit wound bigger than the entry wound, possibly ripping half the wall apart due to said energy transfer on it’s way out. it is still less damage than the bullet exploding in the body / object however.
A rather weird example for this: we had a case of an accident with a particle accelerator back in 1978 a man named Bugorski was supposed to fix something on a particle accelerator.. it hit him through the head… this particle was going so fast it literally phased through him without visible damage however you can still somewhat get an exit wound in terms of radiation. The back where the particle exited is still much more affected than the entry was.. which goes to show even at ultra high speeds this energy transfer happens… just the faster and smaller a projectile the less chance it has to interact with stuff.
So yes if an object is fast enough it can practically just punch a tiny tiny hole.. but the effect of a bigger exit wound still happens… fun fact it is why gamma radiation is so mean.. gamma radiation is just piercing so much and it still exerts enough energy to cause bits of dna damage…in a way we are looking at a very similar phenomenon as getting shot by a fast bullet.. just gamma radiation is incredibly small so the damage is proportionally small scale..as it is just a really really really small bullet in that sense.
Survivability is mostly a function of kinetic energy (KE) transfer.
KE=0.5*mv^2. So a fast-moving .50 cal bullet has much more energy than a slow-moving piece of rebar. Also the bullet is designed to transfer more of that energy (by air cavitation, mushrooming or fragmenting) to whatever it hits than a sharp stick can (it just passes through).
This is the type of question a gun nut could authoritatively answer. I’m not a gun nut but I did fire one long ago and I’m only going on old memories of firing one long ago, so take my info with a grain of salt.
**1 momentum**: the 50BMG can generate 18,000 – 20,000 joules of energy while a rebar going through you (or you falling on it) generates (0.668 lb/ft x 6 ft = 1.814 kg @ 6 meters = 10.9 m/s) (0.5 mv^2) 108 joules. I’m sure my math is bad, but the orders of magnitude alone should convince you the bullet has 2 orders or magnitude more energy (176x). **The rebar would have to be falling at 144 m/s or 324 miles per hour to hit you with the same energy**. Keep in mind this extra energy (and speed) means it’s not just going through you faster, but it brings a [SHOCKWAVE](https://www.nasa.gov/mission_pages/galex/20070815/f.html) with it, and that’s gonna tear up more stuff.
(sorry about the switching units, my brain is just crazy with units)
**2 TUMBLING (STOPPING POWER)** Also is the fact a rebar will probably to straight through you most of the time, while bullets will often [TUMBLE](https://en.wikipedia.org/wiki/Stopping_power), which just creates an awful mess.
hope that helps.
>How is it
Speed. The bullet, while smaller in diameter and lower in weight, is moving far, far faster than the rebar. That speed means that when the bullet hits, [lots of energy is dumped into the target,](https://www.youtube.com/watch?v=5J9hCDr21mo&t=228s) creating a temporary wound channel (the big ballooning you see at the beginning) along with a permanent wound channel (what remains after the temporary wound channel collapses) much larger than the actual diameter of the bullet due to how the temporary wound channel stretches, tears, and destroys tissue along the path of the bullet.
For a simple demonstration of this idea, think of the difference between slowly lowering your hand into a pool of water and slapping it as hard as you can. You’re using the same mass and size (only the speed changes) but have two wildly different results.
Two reasons 1) the speed of rebar is nothing compared to the speed of the bullet 2) bullets have a popcorn effect when they enter bodily tissues, they expand and cause destruction globally as opposed to the rebar which maintains its structure and cleanly pierces this tissue
It’s the speed that makes all the difference. Bodies being mostly water, and water being mostly incompressable, when a bullet flies through you in less then the blink of an eye, it essentially creates something close to a sonic boom in your body. Everything that was in the bullets way is forced to move at insane speeds, transferring that energy into everything around it.
Buck/bird shot from a shotgun within like 10′, acts as a solid object even though it’s a spread of pellets for the same reason.
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