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 12-11-Of beer, apples, joules and motorcycling
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Female Junior Member
26 Posts

St. Louis, MO


VFR 750F
Peer Review: Blocked

Posted - 03/01/2011 :  9:27 AM                       Like
We've seen it time and time again in the movies or on TV: the villain-and sometimes the hero-is hit over the head with a beer bottle. If it doesn't knock them out, they are at least dazed and confused. So it's a little odd that it wasn't until last year that someone asked to give definitive proof that a beer bottle, used as a weapon, could actually crack a human skull. Isn't that a...wait for it...no-brainer?

Apparently not-or at least they wanted scientific and not Hollywood proof. According to a paper published by one of Switzerland's leading forensic pathologists and frequent expert witness, Stephan Bolliger, et. al., determined whether a beer bottle could crack a human skull.

According to The Ninth Annual Year in Ideas, "Other scientists had already calculated how much energy it takes to crack the human skull - between 14 and 70 joules, depending on the location - so all Bolliger needed to do was to take the same measurements on a beer bottle. "If the bottle is more sturdy than the skull," he says, "then the bottle will win, and the skull will break." Simple as that.

Which, I have to say, surprised me in a couple ways. First, the range is wide-I guess some people really are more hard-headed than others. Actually, it depends on what part of the skull is hit as some parts are stronger than others.

But 14 joules doesn't seem like much since, according to Wikipedia's entry on joules, one joule is "approximately the energy released when that same apple falls one meter to the ground" or "the kinetic energy of a tennis ball moving at 23 km/h (14 mph)."

Just to put some science behind a couple other things we take for granted an average apple weighs 5 ounces and the mass of a tennis ball is between 56.7-58.5 g. And a meter is 3.28083 feet. Iow, a meter is shorter than your head is above the ground when you're sitting on most motorcycles.

Would 14 joules be the energy released when 14 apples fall one meter or 14 tennis balls traveling at 14 mph? Probably not-but sure as shooting, your head is heavier than an apple and a tennis ball. In fact, the average human head weighs between 8-12 lbs, which means your head likely weighs as much as 26-38 apples or between 62-64 tennis balls.

But we were talking about whether a beer bottle can break your skull. Speaking of which, your head weighs between 20-30 empty bottles or between 7 and 10 full ones. The next time you're sitting around drinking a few bruskis you can trot out that little factoid-though I certainly don't recommend drinking enough full or empty ones to make your point.

Now, really, let's get back to Bolliger's research into skull cracking: He and his fellows found that, "Full bottles broke at 30 J impact energy, empty bottles at 40 J. These breaking energies surpass the minimum fracture-threshold of the human neurocranium. Beer bottles may therefore fracture the human skull and therefore serve as dangerous instruments in a physical dispute."

The NYT's article on the year in ideas points out that an empty bottle is stronger by a third-and thus more lethal. That's rather counter-intuitive. The article explains it this way: "The beer inside a bottle is carbonated, which means it exerts pressure on the glass, making it more likely to shatter when hitting something. Its propensity to shatter makes it less sturdy - and thus a poorer weapon - than an empty one."

So there you have it-Hollywood gets it right: empty or full beer bottles can crack your skull open. Doh. Which seems to be a long way around to say something we figured was incontrovertible in the first place.

Except...my guess is that you sure wouldn't go running your head into a beer bottle on purpose. And, if you knew you were going to be hit over the head with a beer bottle-full or empty-you'd avoid it. That's a no-brainer, too.

Motorcyclists' heads weigh so much more than apples or tennis balls or beer bottles whether they be full or empty and we travel so much faster than 14 mph and sit higher than one meter from the ground. All those things are as obvious as beer bottles can crack skulls. Doh!

I bet the ground-or a vehicle, utility pole, guard rail or tree exerts a lot more than 30-40 joules of force when your head runs into it-especially since it only takes between 14-70 joules to crack your skull. It makes a beer bottle look like a caress from a feather-and that's another Doh!

Yet so many people who wouldn't court a bar fight when a bottle of Bud is involved set out on the road with no protection on their skulls. Not to mention those who head out on the road after imbibing the Bud. That's as smart as picking a bar fight where everyone has a case of beer bottles aimed at your head and you have nothing but your charming smile.

Motorcycle helmets, though, are built to withstand 67.6 to 150 joules (depending on the test). Iow, it's like being hit with 1.69 to 3.75 empty beer bottles at once.

Granted, it doesn't seem like much protection-but tell that to the guy in the bar fight who's hit with just one empty bottle...

So unless you have an apple or a tennis ball for a head, wear a helmet. It seems like a no-brainer, doesn't it? Doh!
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