Why do people often fall to the ground after being shot? At first read, the answer is obvious: Because they've been shot. Duh! But the issue is actually much more complex.
Sure, if struck in a region vital to standing -- the kneecap, for example -- it makes perfect sense that a person would crumple to the ground. But what would happen if the bullet strikes the chest?
A pervasive Hollywood explanation is that the victim would be blown back, perhaps by as much as a dozen feet if the gun is a powerful one. But this doesn't make sense at all. Newton's Third Law is pretty unequivocal about this: any applied force is subject to an equal and opposite force. So the shooter should also be launched a significant distance in the other direction!
Just in case Isaac Newton was somehow mistaken, the MythBusters put this shoot em' up scenario to the test back in 2005. Firing a .50 caliber sniper rifle -- a really, really big gun -- at a dummy similar in size and composition to the average adult male, they found that the dummy was only knocked back a mere 2.5 inches. Wimpy! So there must be another explanation as to why people often instantly fall down after being shot.
In Stiff: The Curious Lives of Human Cadavers, author Marry Roach asked ballistics expert Duncan MacPherson to shed some light on this mystery. He insisted that the effect was purely psychological. Most people have seen shooting victims instantly collapse on television and are well aware of bullets' deadly reputation. Thus, when shot, their response is to fall to the ground into a relatively "safe" position. To further corroborate his conjecture, MacPherson brought up an animal example. Assumedly because they don't understand what it means to be shot, deer hit through the heart often continue running for up to fifty yards, only collapsing when blood loss renders them unconscious.
Further substantiation for MacPherson's reasoning comes from a couple of fascinating historical anecdotes. In the early twentieth century, expeditionary American troops were fighting against Moro tribesmen in the Philippines and against the Boxers in China. In battle, they were flabbergasted to find that their .38 caliber rifles and handguns could scarcely stop the charging enemy. Often, as many as four hits were necessary to bring a combatant to the ground. It's likely that naiveté about the damaging effects of guns, coupled with battle-fueled adrenaline, rendered the Moros and the Boxers disconcertingly impervious to bullets.
In both cases, the American soldiers' solution was simple: do more damage. Blood loss and tissue mutilation are amazingly effective at heeling an enemy. Against the Moros, the troops utilized guns that fired bigger bullets. Against the Boxers, the Americans simply fired bullets more quickly. Machine guns helped with that.
But many experts don't subscribe to the psychological explanation of why people fall when shot, instead preferring one that's neurologically based. Roach spoke with neurologist Dennis Tobin, who theorizes that an area of the brain stem called the reticular activating system (RAS) can become overloaded by impulses precipitated by intense pain. Thus, the agony of being shot triggers the RAS to send out a signal weakening the muscles of the leg and causing the person to collapse.
There's also a slightly different take on the neurological explanation. Bullets, when they strike a person, create concussive cavities in the surrounding tissue that swiftly close after opening. Such a shock may send a message to the brain that something is devastatingly wrong. In turn, the brain shuts everything down, entering a "safe mode." A couple of animal studies loosely back this explanation. The researchers in both instances found that bullets (or high-energy missiles, as they called them) impacting the thighs of pigs and dogs send a powerful pressure wave hurtling to the brain, one that can actually damage the hypothalamus and hippocampus.
For now, a 100% satisfactory explanation for why people collapse when shot remains elusive, and likely will remain so for a while. I don't think it's very high on a lot of scientists' to do lists. Nor do I predict that many people will volunteer for a study where they will get shot.
But hey, you never know; "Get shot for science!" does have a nice ring to it.
Primary Source: Stiff: The Curious Lives of Human Cadavers, Mary Roach, 2004
(Image: .44 Magnum via Shutterstock)