Of beer, apples, joules and motorcycling

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 counterintuitive. 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!

Explore posts in the same categories: Motorcycle crashes, Motorcycle fatalities, Motorcycle helmet use, Motorcycle injuries, Motorcycle Safety, Uncategorized

23 Comments on “Of beer, apples, joules and motorcycling”

  1. Jeff Brenton Says:

    One of the recurring arguments against helmets are that they’re only good to 14MPH. “What good are they if you’re going 70?!?”

    Well, it’s the FALL that the helmet works on, since the ground is the first obstacle you’re likely to hit. Watch those high-side videos on YouTube, and you’ll see that the head hits the ground from 6-15 feet vertically, not 100MPH. It’s really quite rare to hit something horizontally before a lot of speed is lost.

    But a fatal head injury can occur by tripping as you step away from the bike.

  2. wmoon Says:

    Jeff, I hope I’m not understanding what you’re talking about here because velocity is not lost by falling vertically–ask any skydiver! : ) And hitting a solid, fixed object is not rare at all when it comes to motorcycle crashes–nor is the ground as innocent a thing to hit as you portray it as. It is also a mistake to assume the majority of crashes turn out like highsides–or lowsides–on a track.

    The helmet doesn’t come into play in the FALL. It comes into play in the process of stopping after you’ve fallen. Helmets work when your head hits anything–whether it be the ground or vehicle or a pole, etc. So I’m not sure what you’re talking about in several ways–but it’s a dangerous misunderstanding you have:

    There’s two main things that “impact” the kind of injury we’ll sustain: The velocity and the change in that velocity the rider is traveling when the head (in this case) hits a solid, fixed object and the position of the body during the impact–what part of the body hits what and what angle it’s at when it hits it.

    More specifically to your point: it’s the Delta-V, which is the change in velocity at the moment of impact. To put it another way, it’s how quickly the velocity drops to zero—as they say, it’s not the speed you’re going that kills you, it’s the sudden stop at the end. But it’s not necessarily the same speed the rider was going prior to the impact; so if tumbling and rolling, skidding across the ground scrubs off speed (as is common in a low and high-side) then the head may be going considerably slower by the time it hits the ground–or another object. Unfortunately, frontal collisions are by far the most common crash configuration in Multi-vehicle and single-vehicle crashes. So you’re simply mistaken there.

    However, it’s not the speed per se but change in velocity that’s critical (play on words intentional) in determining injury severity. And that’s determined by both how the vehicle crashes and what it hits. For example, if a rider strikes a softer or movable surface, some of the rider’s kinetic energy is transferred to the other object in the instant of impact. For example, if the rider is going 20 mph when he hits a wall of hay, his Delta-V will be considerably lower because the bales absorb a great deal of that energy and forward motion.

    On the other hand, if he hits a brick wall, the change in velocity is the full 20 mph because bricks don’t give and so they don’t absorb the kinetic energy. In other words, it’s not the height–unless the height adds to or subtracts from the velocity which is highly unlikely in terms of 6-15 feet vertical. Now if the rider travels even six feet HORIZONTALLY before impacting anything, they will lose some speed.

    Nor is it just the speed but what the rider hits that affects Delta-V. When it comes to injuries, the lower the Delta-V, the better.

    For example, when it comes to hard surfaces, a 10 m.p.h. change in velocity could be compared to hitting the ground after falling off of a step ladder–or your 6′ reference. A 20 m.p.h. change is like falling off a one-story building, and a 30 m.p.h Delta-V is like falling off a three-story building. But once again, what part of the body–and at what angle–will make a huge difference in what injuries occur.

    Your understanding of a motorcycle crash is also limited. In fact, riders generally sustain several impacts–the first is generally the motorcycle with X (except in the case of high-sides), the second is the rider with the motorcycle–the rider often hits part of the motorcycle itself. Then the rider hits an object, if there’s one involved, at least once and then the ground at least once–but more likely more than once. So there’s at least three and often five or more impacts during a crash. During any of these the head may sustain an impact–and rarely in the same place.

    So yes, it’s a big deal that helmets don’t prevent fatal external impact injuries at speeds over 13 mph–and it’s irresponsible for people to minimize that or deny it. Helmets are only 37% effective at preventing fatal injuries and 25% effective at preventing less severe ones–in part that’s because internal injuries (coup-contra-coup and axial rotation injuries) are among the very worst and often fatal or at least debilitating injuries there are. But 13 mph or the relatively low prevention rate are still a damn sight better than nothing at all, imo.

    It concerns me that you–as a motorcycle instructor–are so misinformed about crashing and helmets and conceivably has told students similar things to what you said here. Because if you do tell them stuff like you said here you’re misleading them and could be misleading them to feel that they are safer than they are. And it’s really a mistake and highly irresponsible if you lead them to believe that their crash will be like the ones on a race track.

  3. irondad Says:

    In order to be totally scientific, perhaps we should compare the risk of hitting our heads on solid objects while riding versus the risk of getting hit by a beer bottle. It might come to pass that the “water hole” crowd should put their helmets on when entering the bar. Of course, that precludes a full face. I’m presuming that most beer bottle impacts come from the top and not the front?
    ( tongue firmly in cheek, of course! )

    Interesting approach to the helmet argument. You have a lively and creative mind. I teach ART and was sorry things worked out that I wasn’t teaching when you came up here. Now that you are farther away, the chances are less, but I would love to meet you in person some time. I’m pretty sure we would hit if off.

    Merry Christmas!!!

  4. Bjorn Says:

    I always wear a helmet on a motorcycle or bicycle. I lecture my kids to wear theirs when on their bicycles. I make the point that you are less likely to sustain an injury if you wear protection than if you don’t.
    I also support the right of riders to choose whether or not to wear a helmet. I figure if you can’t see the benefits, we are better off without you in the gene pool.

  5. wmoon Says:

    Let natural selection do its job.

  6. wmoon Says:

    IronDad, I agree we are unlikely to get hit on the head by a beer bottle while riding–though once while riding in Santa Ana winds I was hit in the faceshield by a board and only the faceshield protected me not just from injury but from crashing and further injuries.

    ART is a great course and I’m glad to hear you’re teaching it. Wish I could get out there sometime and take it as well as meet you and more of the great Oregon instructors.

  7. Dave B Says:

    Jeff’s 14 mph myth is widespread among MSF instructors and many riders. The subject is a complicated discussion and you did a good job of explaining it as best as possible in layman’s terms.

    Like much research data, many people just browse through it and come up with an assessment and tell others about it. Usually the ones against helmet laws spread the 14 mph myth. Personally, I’d rather be wearing a helmet no matter what speed I’m going. I was once parking my motorcycle on gravel, slipped and slammed the side of my head on the ground. If I wasn’t wearing a helmet, I’m sure I would have been hurt seriously. That’s why we tell BRC students to make sure they’re wearing their helmets while sitting on a parked motorcycle.

    I’m all for natural selection but not when I’m responsible for the students in my class.

    And the other myth is that Snell-approved motorcycle helmets are better than only DOT-approved helmets.

  8. gymnast Says:

    Wendy, great article and your response to Jeff’s comment above is not only an opportunity to further expand your points,it is an article in itself.

    Far more readable than boring technical stuff such as this http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.bioeng.2.1.55?cookieSet=1&journalCode=bioeng

  9. vstromer Says:

    Not trying to speak for Jeff, but what I interpreted his message as was that forward velocity is not that important when you measure the effect of a head slapper when crashing a motorcycle. The head is dropping, or worse being whipped, onto the ground from a given height. Assuming the crash is just the motorcycle falling over and the head striking the ground (say the rider locks the front wheel during braking and crashes), forward speed doesn’t affect initial head impact as the side of the head contacts the ground. It is (roughly) the same impact whether the rider is going 10 mph or 80mph. I use this logic on the “helmets don’t work over 14 mph crowd.”

  10. wmoon Says:

    Vstromer, Here’s where your argument “falls” down: if you sideswipe a wall at 10 mph or 70, would the the effect would be the same because the angle of hitting it is the same? The vertical fall does NOT negate the kinetic energy due to (forward) velocity.

  11. wmoon Says:

    Dave, You could also tell the students that the skull is thinnest at the sides of the head–which means that it can be more easily injured–than the thicker skull on the forehead and upper back of the skull). But why do you say the 14 mph is a myth (but iirc it’s above 13 mph where fatalities begin to occur)?

  12. Dave B Says:

    Bad choice of words on my part. There’s a few phrases out there that need clarification; “Loud pipes save lives” and “Helmets don’t work if you’re doing more than 14 mph” are a few of them. You did a good job explaining the latter and will use it as a handout with some editing. (From now on, I’ll try to comment when I’ve had more than three hours sleep).

  13. Jeff Brenton Says:

    Wendy, it’s hard to get me to take offense, so pick away at my responses as you see fit. Especially when it brings out so much more to the discussion. Personally, I don’t mention the whole 14MPH scenario. I do get to respond to it from time to time.

    The argument about swiping a wall doesn’t negate considering “just” the vertical component of a crash; in fact, it shows that we’re really talking about the components of a complex system. The “impact” velocity that the helmet has to deal with swiping the wall is exactly the same as a similar “swiping” of the ground. In both cases, the collision absorbs some of the forward velocity, but the impact isn’t all 70MPH worth of energy.

    The fact is that helmets are designed around that 90th-percentile crash described in the original Hurt report. Those numbers have been confirmed by later reports by others. That means helmets are going to work on decreasing the delta-V of multiple 10-20 FPS impacts, rather than one 80 FPS impact.

    If the classroom discussion starts to wander into the “dangers” of wearing a helmet, I relate the story, given to me by another instructor and former EMT, who responding to a fatal motorcycle crash… The “crash” occurred when the rider stopped to talk to friends. He dismounted, and was leaning against the bike when it fell over. He hit his helmetless head against the curb, and died. “Once you leave this class, whether or not you decide to wear a helmet is your decision. We just want it to be an informed one!

  14. wmoon Says:

    Jeff, as the entry made very clear, it doesn’t take much energy/force to crack a skull. As someone who sustained a concussion as a passenger when the fellow low-sided on sand going at the most 5 mph when he did–but a curb was right where my head landed–I appreciate that helmets are valuable but I’m not sure what the point of the anecdote you tell your students is–we should never take helmets off until we’re in our beds?

  15. wmoon Says:

    The whole helmet issue (as is all of motorcycle safety) is rife with easy and misleading ardently believed statements, isn’t it? I agree that the 14 mph thing is one of them.

    Another one that really irritates me is the one that helmets snap necks. or cause basilar fractures. I’ll have to write about that one someday.

  16. vstromer Says:

    I’m with you on the snapped necks and basilar fractures. The anti-helmet crowd always seems to bring this up, usually citing some “authority” they found on the internet. Just applying logic, it would seem that a crash with enough force to cause these fatal injuries to a helmeted rider would certainly be fatal to a non-helmeted rider as well.

  17. gymnast Says:

    Hmmmm. A Leatt type device for the unhelmeted rider. http://www.leatt-brace.com/

  18. wmoon Says:

    um….if you weren’t making a joke, I don’t think that product is supposed to do what helmets are supposed to do.

  19. Bjorn Says:

    The Leatt device is designed to prevent a helmeted head from being pushed beyond the necks ability to bend. Over here in Australia they are recommended equipment in many sports.

  20. gymnast Says:

    Bjorn. I suspect that an unhemeted rider wearing a Leatt device and suffering and energy exchange of sufficient force at an unfortunate angle could, potentially, have the remains of their head and neck substantially displaced. A turtle pulling it’s head back into it’s shell comes to mind.

    On the other hand, sometimes when I see a “salty” unhelmeted rider I am reminded of an ostrich, burying it’s head in the sand.

    In either case, I hope that my use of irony and sarcasm are not mistaken for anything other than gallows humor. Having been an EMT-A while teaching the same subject for several years may have had the effect of overexposure to reality.

  21. Bjorn Says:

    Gymnast. You’re right, it would provide a nice fulcrum for levering off an unhelmeted noggin.
    I was just being the class information monitor.
    I understand that there are some here who are the equivelent of Rider Safe trainers and want to educate the newest riders into safe practices. That said, if someone has so little understanding of physics and the abrasive qualities of tarmac that they think no helmet, shorts, T shirt and thongs (the footwear not the undies) are appropriate riding gear, They should be encouraged, as letting them breed is equivalent to pissing in the gene pool.

  22. wmoon Says:

    Bjorn, I have long maintained that the helmet issue isn’t about helmets at all–or very little about helmets and very much about other things. And I mean that on both sides of the argument. There’s those who put way too much faith in a helmet’s ability to protect them and those that put too little. I don’t think that any instructor believes that sans-gear is appropriate gear, though.

  23. Bjorn Says:

    Wendy, I’m not under too many illusions as to a helmet or other gears ability to protect the user in all situations. However, after nearly twenty years on the bike and my share of falls both on the road and track, I will bet my skin and mental wellbeing on helmet, leathers and back protector.
    I wont claim to be a saint, having road tested stuff at silly speeds in minimal gear when I was a mechanic, years ago.
    Here in Australia we have more stringent road safety legislation, probably due in part to the fact we have a national health scheme that has no opt out clause if you wish to take extra risks. Helmets are mandatory for motorcyclists, cyclists and even those annoying litle scooters with skateboard wheels.
    Helmets being a given, in the state of Victoria the road safety authority promotes the wearing of leathers as a desirable thing.
    The whole debate really comes down to peoples view of personal freedom; it is a idealogical debate rather than a safety issue.

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