copper,
Here is an answer from a site named The Straight Dope:
http://www.straightdope.com/classics/a950414b.htmlDear Cecil:
Every so often you see it on the news: streets full of Middle Eastern men indiscriminately firing guns straight up into the air. If I learned anything from physics class, it's that what goes up must come down. I'm certain the returning projectiles don't float harmlessly to earth and wonder how often they plunge into bystanders. --Kathy Johnson, Madison, Wisconsin
Cecil replies:
Those Middle Eastern men. You want to shake them and say, guys! Is this the safe and sensible way to celebrate? Can't we just say "hooray!" and "whoa, baby"?
But you raise a good point. How dangerous is this really? The question is controversial. Let me lay it out point by point.
Datum 1. At first I thought being struck by a bullet falling straight down would be no worse than getting hit over the head with a two-by-four--not the average guy's idea of fun, but not fatal either. What goes up must come down, but it needn't do so at the same speed. You run up against what's known as "terminal velocity." A bullet fired straight up will slow down, stop, then fall to earth again, accelerating until it reaches a point where its weight equals the resistance of the air. That's its terminal velocity.
For further insight, we turn to Hatcher's Notebook (1962) by Major General Julian S. Hatcher, a U.S. Army ordnance expert. Hatcher described military tests with, among other things, a .30 caliber bullet weighing .021 pounds. Using a special rig, the testers shot the bullet straight into the air. It came down bottom (not point) first at what was later computed to be about 300 feet per second. "With the [.021 pound] bullet, this corresponds to an energy of 30 foot pounds," Hatcher wrote. "Previously, the army had decided that on the average an energy of 60 foot pounds is required to produce a disabling wound. Thus, service bullets returning from extreme heights cannot be considered lethal by this standard."
If 30 foot pounds doesn't mean much to you, the bullet made a mark about one-sixteenth of an inch deep in a soft pine board. About what you'd get giving it a good whack with a hammer. Note that we're talking about bullets shot straight up here. If the bullet is fired more or less horizontally, it may not lose much speed before returning to earth and could easily kill someone.
Datum 2. Then someone sent me an article from the Los Angeles Times about the problem of falling bullets in L.A. around New Year's and the Fourth of July. According to the article, doctors at King/Drew Medical Center, a major L.A. trauma center, published a report in a medical journal (Journal of Trauma, December 1994) saying that between 1985 and 1992 they treated 118 people for falling bullet injuries around New Year's Eve or the Fourth of July. Thirty-eight of the victims died.
"There is some skepticism about the numbers reported by the King/Drew team," the article continued. "The Los Angeles County Sheriff's Department and the Los Angeles Police Department--which serve a vastly larger area-- reported only about half a dozen deaths in the same period. . . . Other hospitals contacted by The Times . . . reported few cases."
King/Drew handles a lot more gunshot cases than other L.A. hospitals. But the King/Drew doctors also used fairly liberal criteria to identify falling-bullet victims (no gunshot heard or weapon seen, wound consistent with bullet falling from above, etc.). Given how confused trauma victims and witnesses often are about what happened, the numbers reported are probably high.
Datum 3. Still, the question isn't how many people get injured or killed by falling bullets, it's whether such things are possible at all. On further investigation, it appears the 60 foot-pound injury threshold cited by Hatcher may be misleading--a falling bullet's kinetic energy (foot pounds) alone is not a good predictor of the speed it needs to inflict a wound. B. N. Mattoo (Journal of Forensic Sciences, 1984) has proposed an equation relating mass and bullet diameter that seems to do a better job. Experiments on cadavers and such have shown, for example, that a .38 caliber revolver bullet will perforate the skin and lodge in the underlying tissue at 191 feet per second and that triple-ought buckshot will do so at 213 feet per second.
Mattoo's equation predicts that Hatcher's .30 caliber bullet, which has a small diameter in relation to its weight, will perforate the skin at only 124 feet per second. It's easy to believe that such a bullet falling at 300 feet per second could kill you, especially if it struck you in the head. In fact, maybe I need to rethink my dismissive comments about the danger of throwing a penny off the Empire State Building, although I still think the penny's tumbling in the updrafts would render it harmless.
So, Middle Eastern men, gang bangers, etc., listen up! It has been scientifically shown that firing guns into the air for entertainment is not a good idea. Please stop right away. Also knock off with the holy wars and random violence. Thank you.
--CECIL ADAMS
