It is a familiar trope in any violent action scene. Some gets shot and the impact causes the person to fall back, sometimes even thrown into the air or, more spectacularly, propelled backwards through a glass window. Filmmakers seem to love such scenes but it would never happen in reality. This is because although the bullet is traveling at high velocity, it also has very small mass and so its momentum (mass times velocity( is small, not enough to knock the victim over. At best they might move back a couple of inches
Bullets cause damage by penetrating the body and hitting the various organs inside and causing loss of blood.
This article explains why.
Of course, if a person is hit in a part of the body that is a vital necessity to assure that we can stand upright, such as a knee cap, then they will fall when shot. However, if the bullet strikes another body part such as the chest, abdomen, head, arms, etc., would the person fall down or be catapulted backwards Terminator style? Most likely they would not.
In 2005, a TV show called Myth Busters put this theory to the test. They fired a .50 caliber sniper rifle, which is a really big gun, at a dummy that was similar in size to the average adult male. When they shot the dummy, it was only knocked back 2.5 inches, not several feet.
…However, we know from shooting animals, such as deer, that when they are shot they can travel for up to fifty yards. They only collapse after losing enough blood to be rendered unconscious.
…When a human body is impacted by a projectile such as a bullet, the bullet enters the body, crushes and shreds tissue in its path, and creates a permanent cavity called a bullet hole. The energy of the impact of the bullet is dissipated in a shock wave that “flings” surrounding tissue away from the path of the bullet, creating a hole larger than the diameter of the bullet called a temporary stress cavity that exists for about 5-10 milliseconds with a series of gradually smaller pulsations and contractions before the formation of a permanent wound track. The extent of the final wound is determined by the kinetic energy on impact, extent of the temporary cavity and the amount of bullet fragmentation.
Here is the Mythbusters episode that was referred to above.
Here is an animation of the same phenomenon.
It was not always thus. In the 1934 Alfred Hitchcock film, The Man Who Knew Too Much (he remade it in 1956 with the same title), we see two characters who are shot in the chest. Neither of them move at all, let alone stagger back. They just know that they have been hit and slowly fall to the ground. So when did this trope of massive recoil start?
The real killer (ha!) fact that should alert you to the falsity of this trope is that by Newton’s Third Law of motion, if the gun could impart enough momentum to the bullet to send the victim flying backwards, the recoil momentum should send the shooter flying in the opposite direction. But that would not make for satisfying viewing. So we see the shooter calmly walking away after knocking the opponent off their feet. In these days of evermore spectacular shooting scenes, this myth is likely here to stay.
“if the gun could impart enough momentum to the bullet to send the victim flying backwards, the recoil momentum should send the shooter flying in the opposite direction”
This is pretty funny, and I do wonder how that myth got started? Did some director or screenwriter just not know, or did someone want a more spectacular effect and just throw that in? One meaning of the phrase “blown away” is now “being shot”: did that come from watching the movies?
Are shotgun blasts any different? Movies really like to have someone knocked backwards or through a window by a more “powerful” weapon. Shotguns have many little pellets hitting the body in slightly different places, but the pellets are all so small, I don’t think that would work either.
I saw a TV show once that had some soldiers in combat, and one was shot at and spectacularly fell backwards. His buddy thought he’d been killed, but the sergeant said “No, a bullet would go through you, not knock you down. He’s been hit in his (bullet-proof) vest.” Which, in the show, turned out to be true. I wonder about the physics of that, could being hit in a resistant material knock you down?
“could being hit in a resistant material knock you down?”
The momentum of a nato standard round is similar to being hit in the chest by a bowling ball doing about 10mph. I think if that hit me and that load was spread over my whole chest, I’d go down.
garnetstar,
Being hit while wearing a bullet proof vest does give you a slightly larger ‘kick’ but nowhere near the amount needed to knock you back. The Mythbusters video at the 3:25 mark does the test.
The fact that shotguns fire a lot of small pellet does not make a difference as long as all the pellets strike within a narrow region, since their momenta add up. It is the total momentum imparted by the gun that matters most.
Does this validate the scene in Is Paris Burning where a German general takes a machine-gun burst in the chest at point-blank range (from Burt Lancaster, no less!) and falls forward?
Pierce,
For most gun shots, which way the person falls depends on factors other than the shot, such as which way the person was moving or leaning.
Gyrojet ammunition (now an antique) solve this f=ma ‘kickback to the shooter’ by accelerating after leaving the barrel. But in order to do this you were *hoping* your target was far enough away that it had time to accelerate to full speed and that your microrocket was accurate.
I’ve heard stories about Sir Christopher Lee getting into arguments with directors over this particular myth. Lee was RAF Intelligence and special forces during WWII, so I think I’ll take his word for what likely happens when someone gets shot over a movie director.
But yeah, this is pretty much my understanding. If you’re wearing a bulletproof vest which will maximize the transfer of momentum to you, and get shot with something relatively powerful, you might stumble back, bit you’re certainly not going to be flung back. The bowling ball reference above… well, it doesn’t sound wrong (I have friends in the Reserves I could ask to be sure) but you also have to remember that the speed of a bowling ball when it gets released onto the lane by a professional bowler is usually about 20mph. So that momentum is about half what you’d get from someone just lobbing the ball at you, meaning it’s a good deal less momentum than a well-delivered punch.
So it’s in the territory of ‘if you’re braced you probably won’t move at all’, and the other above comment about fall direction being more influenced by which way the person was moving or leaning is right. The target’s main direction of fall is going to be down.
Bodies aren’t just sacks of meat, but have neurons and muscles. What is the reaction of these tissues to a bullet passing through? Could it cause muscular contraction?
@jenorafeuer:
That’s because I did the sums, engineer style (in my head, mostly just orders of magnitude). Standard NATO 5.56mm round weighs roughly 12, call it 10 grammes, so 0.01kg, leaves the barrel of an SA-80 assault rifle at 980 call it 1000m/s, so the momentum is 1000 x 0.01 = 10kgm/s. Call a bowling ball 5kg so 2m/s is actually close to 5mph, so I even overestimated a bit. I still think if you’re not expecting it a shove like that could knock you over, but you’re right, if you’re braced it almost certainly won’t.
It’s 30 years since I read about Penn and Teller’s debunk of the Kennedy conspiracies, in their book “The Unpleasant Book of Penn and Teller, or How to Play With Your Food”. Long story short, after Luis Alvarez, they wrapped a melon in fibreglass tape. This models a skull. The general gist is, the bullet doesn’t transfer much momentum to the skull, and the brain certainly doesn’t put up much resistance, but when the bullet and a fair bit of brains leave the skull, that creates a little jet-blast that pushes the skull TOWARDS the source of the bullet. So they tried it.
They got a 6.5mm Mannlicher-Carcano rifle, same as Oswald used.
They got one-inch Scotch glass filament tape, same as Alvarez used.
They got a honeydew melon, same as Oswald ate for breakfast the day he shot JFK.
They wrapped the tape round the melon.
They decorated the melon -- and stated in the book that “We both feel strongly that putting a melon wearing a pink pillbox hat next to the target melon is in very bad taste.” See video.
They did NOT set the melon up 265 feet from the shooter.
They shot the melon with the gun.
They did it with AT LEAST 35 melons. THIRTY FIVE. And I quote:
“Every single melon that moved -- moved toward the gun”.
About a decade later, on season 3 episode 3 of Bullsh!t, they filmed it.
There is ample WWI film footage of British troops going ‘over the top’ into a hail of German rifle- and machine gun bullets that show that when hit a body just falls to the ground.
Depends what you’re shot with. A cannonball or howitzer round would probably move you a fair bit.
There’s a shitload of combat footage from the Ukraine war for anyone who cares to look.
Next: silenced shots are still loud, bullets don’t make ricochet noises unless they actually ricochet (cue the ‘schiiing!’ sound when blades are drawn, so one can tell they are sharp), and car tyres don’t squeal on dirt roads. Etc.
(Ah, the movies!)
I reckon I’d rather get hit with a bowling ball at walking speed than a bullet at bullet speed.
All that momentum transfer is done over a rather small cross-section.
Back in my wayward youth, I went with some acquaintances to a remote area where stolen cars were dumped and saw someone using a WW1 .303 rifle shoot bullets through an the block of an old V8 engine. I mean, right through.
—
Oh, right. https://en.wikipedia.org/wiki/5.56%C3%9745mm_NATO
(those bullets are 4g, which is less than half of 10g)
Bullets cause damage by penetrating the body and hitting the various organs inside
Well, yeah, but it’s also more complicated than that. High powered bullets also cause a lot of damage due to displacement and cavitation. If you get hit in the belly with a .308, for example, there’s a decent chance there will be so much cavitation that your heart will stop/be damaged from the shockwave -- it’s not “hitting the various organs” its basically liquifying a bunch of stuff because water doesn’t compress well, and the shockwaves going through tissue literally rip your organs apart without the bullet having to hit them at all.
I think a lot of people think about knocking a target back, because they’ve seen slow-motion footage of high powered bullets hitting ballistic gelatine, which is all fun and nice until you actually think about it. But something like the aforementioned .308 will knock a heavy block of ballistic gelatine back a foot or more on the table on which it’s sitting. It won’t knock back a human, like, that, but it’ll kill them quickly dead and they’ll fall back with a nudge.
A .308 packs around 2500 foot/lb of energy, which is a lot. There are bigger bullets out there, too, but when you’re talking about that much energy then the question is less a matter of how much energy versus how much energy is transferred to the target. Does the bullet just zip through, or does it make everything splat?
Slow motion studies of ballistic gel show the degree to which energy transfer affects the target’s experience. E.g.: @3:31
https://www.youtube.com/watch?v=qB5OizvSPG4
Also, remember that a human is kind of a lever. If you’re standing and you get hit in the head by a high powered bullet, you’re going to fall in the direction the bullet was going, if there’s significant energy transfer. Get hit in the stomach, and you’ll fold up. Ow. Get hit in the foot, you might fall forward, etc. Every account you read about large battles conveys the fact that bullets and people do weird things sometimes when they interact and the best approach is to avoid the whole issue.
It might actually be better to get hit by the tungsten penetrator from a .50BMG than by a big old bumblebee subsonic .45 hollow point. The dart will zip through anything and not transfer much energy at all, whereas the big blob of lead will fuck you up.
When I was in college a few of us got our hands on some armored glass. This was pre youtube, of course, so we couldn’t just go online and see 1000 videos of people shooting armored glass. We hit it with .22, and we hit it with 9mm and we hit it with a .44mag (that made a great big ugly dimple in it) and then my buddy Mike shot it with his Brown Bess .75 cal muzzle loader. There were pieces of armored glass everywhere. Lots of energy transfer from a big fat musket ball is a horrible thing.
As an amateur military historian who has read way too many journals from the Napoleonic wars, xohjoh2n’s comment at #12 about cannonballs is mighty sobering. There is an account in Cavalie Mercer’s journal of the fight at Waterloo, in which a fellow got hit by a 6lber cannonball and was knocked up into a tree. Another fellow had the top of his head sheared off and continued talking for a while until he realized he was hit, sat down, and died. Marshal Lannes died from a glancing blow of an almost entirely energy-expended cannonball which still “exploded his leg.” There’s another account of a green troop who had the idea of stopping a rolling cannonball with his foot, who was knocked 12 feet or so and landed on his remaining leg.
Whenever we’re talking about kinetic things interacting with bodies, there’s just no good to it, no how.
If I poke you with a stick, you’ll get pushed backwards.
If I poke you with a rapier, you’ll get a rapier through your vitals.
(Physics FTW!)
Next: silenced shots are still loud
Modern silencers are amazing. I have a friend with a suppressed .22 and with subsonic ammo the sound of the hammer falling inside the gun is about all you hear. A little click. It gets expensive but you can silence up to a 9mm that well. The issue is not as simple because a lot of the sound of a shot is the supersonic crack of the bullet. (When I was in basic, I got to work the targets on the range and spent 4 hours with .223s cracking over my head and it is very unsettling) -- I have subsonic .308 win ammunition that sounds about like a .22 fired through a suppressor, and it would still liquify a moose. So, yeah, you’re an Australian, right, so what you know about guns is probably from American movies.
bullets don’t make ricochet noises unless they actually ricochet
That’s true. What happens, often, is that the jacket of a jacketed bullet gets deformed and becomes a sort of a whistle. When that happens they can also spin in some pretty interesting ways. The weirdest bullet sound I can think of was the time I shot a bottle of tempera paint with a 9mm and the paint went non-Newtonian and came back at me along the path of the bullet. AND it was supersonic when it did it, because the camera recorded a weird kind of mushy fluttery sonic boomy thing.
(cue the ‘schiiing!’ sound when blades are drawn, so one can tell they are sharp)
Depends on the sword. Naturally, a wooden scabbarded sword (viking sword, katana, rapier, longsword) makes a kind of wooden dry rustle, but Napoleonic hussars and cuirassiers swords had metal scabbards and you’d definitely get a schiing from one of those. If I still had my hussar’s sword, I’d record it. But, anyhow.
Are swords legal in Australia? I’m assuming because of Crocodile Dundee that big knives are OK…?
and car tyres don’t squeal on dirt roads. Etc.
Depends on the dirt, tires, and speed. But, …. maybe.
Marcus, I do appreciate you riffing. And your minutiae.
Um. Lots of guns here in Oz.
Main difference is that, here, one needs to justify gun ownership.
We only seem meek, gunwise, when compared to you mob.
(When I worked for a rural council, at least half the people used their gun license rather than their driver’s license for identification purposes for formal documents)
I’ve never seen one other than hanging on someone’s wall.
Concealed blade weapons, those are for sure illegal here.
Re sword legality in Australia
Knives and swords laws are set at state level, so varies depending on where you are. Here in Victoria the laws are kind of BS: a roundel dagger is legal, and Fairburn-Skyes knife is not. The laws are mostly an exercise in giving Victorian Police the power to be a nuisance IMO
Backing up what Marcus Ranum said in @18, prior usmc enlisted, and spent a lot of time on live ammo ranges.
Most assault weapons/high power rifles use a relatively small projectile traveling at very high velocity.
So, if you are down range, you will hear the sharp “crack” sound from the projectile creating a tiny sonic boom, and then just after hear the “bang” from the powder discharge. I don’t have much experience with subsonic ammunition. And, if I ever hear that “crack-bang” sound again, outside of a range, I imagine I will be very concerned…
As mentioned above, a round that just up and punches through a body isn’t going to transfer much kinetic energy (it will still do a ridiculous amount of damage due to the shockwaves and gasses following the projectile, as Marcus mentioned. I think that’s why they refer to “stopping power” in reference to hollow points, shotguns, etc. The round expands (“mushrooms” when it hits the resistance of flesh, and transfers more of the kinetic energy to the target. Or, with the shotgun, each individual projectile imparts energy to the target, and there’s probably some square-cube law analogy there…
One minor thing not mentioned, is when someone is firing a weapon, (especially the higher-powered ones…), they are often in a position specifically to brace for and absorb the force of recoil. If the round actually transfers all (or maybe just most?) of it’s force to person in a random position, it’s certainly possible to knock them over, while the shooter is able to remain relatively unaffected, because they took a specific position/stance to minimize the effect of recoil. Also, I don’t have any clue how much this makes a difference, but the standard US issue M16/M4 (at least as of ~20 years ago…), has a spring and a small piston-like assembly in the stock that is intended to reduce recoil.
Cavitation… the wound canal of high-speed .556 bullets are even worse than for old .303 or 7.62mm bullets.
.
When Sweden adopted the .556 bullet as standard they chose/developed a variant that does not wobble as violently to keep the wound canal somewhat essier for surgeons to fix.
WWIII was expected to be short enough that no soldier undergoing major surgery would return to the battlefield.
It is not enough for a vest to stop a bullet, it needs to spread out the impact somewhat to reduce the injuries. This can be the difference between a nasty bruise and punching the chest so violently the heart stops.
The development of protective vests is a complex subject with both weight and cost being limiting factors.
As for stopping a .50 cal bullet, no vest can do that. But the force may be enough to push the (now dead) soldier backwards. I have not performed empirical testing.
Heh. So serendipitously timely: