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Head injury without a helment

  1. Jul 31, 2011 #1
    i work in a bike shop - i am always getting questions about helmets - what good are they as they are only made of foam -

    i have been trying to find a way to explain just how fast your head is going when it hits the ground when you fall off a bike and what force is exerted upon your 10 pound head without a helmet - then compare that to wearing a helmet and what the difference would be -

    i did figure out that without a helmet its somewhat like a 5 pound sledge hammer being dropped from 14 feet on your head - pardon my physics - lol - is this somewhat right???

    i am a believer in helmets - i have broken a few and would hate to think what would have happened without one - its hard to sell them to people who look and say - its only foam - big deal - like the guy said in the store the other day - what can that do - its just a sales game ....... please help me out here -

  2. jcsd
  3. Jul 31, 2011 #2
    The reason helmets save lives is because of that foam padding. Upon collision the foam padding compresses, which increases the time of a collision, which means a smaller force (over a greater time period) is applied to your head to slow it down. If you were not wearing a helmet and the padding was not there the force would have to be much greater because its applied to your head in a much shorter amount of time.
  4. Jul 31, 2011 #3
    yes - i understand that completely - i need some numbers - speeds - that will allow people a frame of reference -
  5. Jul 31, 2011 #4
    People dying of stupidity is an important force driving the evolution of the human race. By protecting individuals from themselves we are short-changing future generations. But I guess that's somewhat off topic.

    I find that most people don't respond to arguments based on physics. Just ask if they were about to get hit in the head with a baseball bat would they wand the helmet or not. I think most people will agree that it will offer some protection, though they may not appreciate just how much. Perhaps show them a helmet that has been crashed and explain that any energy used to damage the helmet is no longer available to damage their head.
    Last edited: Jul 31, 2011
  6. Jul 31, 2011 #5
    Sure, I could give you a mathematical explanation.

    So say your head with a mass ([itex]m[/itex]) of about 5 [itex]kg[/itex] is traveling with a velocity ([itex]v[/itex]) of 5[itex]\frac{m}{s}[/itex] straight towards a brick wall. Over the course of the entire collision, from v=5[itex]\frac{m}{s}[/itex] to 0[itex]\frac{m}{s}[/itex], there exists an impulse ([itex]I[/itex]). Impulse is equal to the change in momentum, but it is also equivalent to the force ([itex]F[/itex]) multiplied by the time of collision ([itex]t[/itex]).

    [itex]I=m \Delta v=Ft[/itex]
    The delta ([itex]\Delta[/itex]) denotes the change in the velocity (in this case its 5 [itex]\frac{m}{s}[/itex]). That multiplied by the mass gives you the change in momentum.

    The impulse for this collision can be calculated to be [itex]I=5*5=25 kg \bullet s[/itex]. Because this impulse will always remain constant for this collision with our without a helmet you can use it to calculate both cases. Mind you I'm just pulling these numbers out of my ***, so lets say the time of collision for without a helmet is [itex]t=0.05 s[/itex] and the time with a helmet is [itex]t=0.5 s[/itex]. Use the impulse equation to solve for force with both instances and you'll get that the force without a helmet is 500 Newtons, or 112.4 lbs of force. With a helmet you get only 50 Newtons, or 11.2 lbs of force. Something that I would imagine is much easier to survive. But again, I did just make up these numbers.
  7. Jul 31, 2011 #6


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    The helmet also distributes the force over larger contact area & wider support base at the head. This reduces local pressure and deformation of the skull.
  8. Jul 31, 2011 #7


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    Exactly. If people don't respond to arguments pull out a baseball bat.
  9. Aug 1, 2011 #8
  10. Aug 1, 2011 #9

    Ranger Mike

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    I suggest you look up ABATE...the anti helmet law nation wide organization to block any mandatory helmet laws...being a former biker..as in Harley..not schwin...I have seen both sides of the argument..there is substantial data on injuries...in my opinion..ref bikers..90 percent of injuries reported are lower extremities...i always get a laff out of seeing that $200 full face helmet on that weekend honda rider in flip flops and shorts going to the near by 711 on a Saturday morning...dumb...
    most bikers like the no helmet thing because riding a scoot is all about survival...when you think you mastered a scoot..watch out..your going down...so the biker likes the ability to see 180 degrees, peripheral vision is absolutely requires as is HEARING..why block off one and one half of your senses wit ha helmet...two more things..i lost a bro who had a cop helmet and a bee got in between the strap and the skull..he went down..another bro almost wiped out due to excessive heat on the brain pan..temps really amp up under the skid lid..
    so fellow bros..continue the fight and remember

    helmet laws suck

    Ranger Mike..former Road Captain..HHMC
  11. Aug 1, 2011 #10
    I've got to say that I don't agree with you there Mike. Most bike accidents occur at junctions, cars pulling out becuase they don't see you.

    When you are flying over a car bonnet with your head appraching the ground or a lamp post. I know i'd rather have my head protected.

    Just like seatbelts, helmets can and do save lives. Anyone not wearing leathers and a helmet on a bike is an idiot. On saying that I live in the UK, even in summer it isn't outrageously hot. But if you want to stay cool , get a car with aircon.
  12. Aug 1, 2011 #11

    Ranger Mike

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    on this Chris..we must agree to disagree..Most stats on the subject are from the insurance lobby...and are suspect..for me...I quit riding years ago...I do like the fact that in Ohio. we shut down the capitol when 25,000 smelly, flea infested, mostly drunk and stoned bros swept into town and were EVERYWHERE...tied up traffic, camped out all over the place..Columbus ran out of beer at one point and they have a Budwieser brewery there...there thousands of us...the Ohio legislature did not move ahead with the mandatory lid law...it was a moderately peaceful civil protest...and it is about freedom of choice...
    but thanks Bro..you have great advice and insight...
  13. Aug 1, 2011 #12

    I like Serena

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  14. Aug 1, 2011 #13
    I had my bicycle helmet on the desk, so I guess that's why I looked up bicycle info. :redface:

    I think I Googled "bicycle helmet impact study", so "http://www.google.com/search?q=motorcycle+helmet+impact+study"" should find similar... yep:
    [PDF] http://www.smarter-usa.org/PDF DOCUMENTS/Helmet_Research.pdf
    [PDF] http://www.snellfoundation.org/docs/articles/hic/Helmeted_MC_JTrauma.pdf
    (and plenty more)

    Google Scholar adds more detail:
    http://scholar.google.com/scholar?q=motorcycle helmet impact study
    Last edited by a moderator: Apr 26, 2017
  15. Aug 1, 2011 #14
    Let's not forget the protection from low impacts with jagged edges such as tree branches, or scruffs from the sidewalk or street surface as you slide along - makes you wish they had helmet type protection for other body parts.
  16. Aug 1, 2011 #15
    I've never had an issue with helmets causing blind-spots, or reducing my hearing. If anything, helmets improve my hearing. After 30 minutes or so of wind noise at highway speeds without a helmet, I can barely hear! Heat is only a problem when standing still. Air is directed all around my head, and flow is adjustable. Riding to Lake Isabella in 115°F weather (no exaggeration), I sprayed water on the helmet lining every time I stopped for a drink. Worked wonderfully. I do the same thing when off-road riding.

    I'm 47, and I've been riding on the street since before I had a drivers license. I actually made a 2000 mile cross-country trip with my dad when I was 15 (must be 16 for a license in California). I haven't kept records, but I can remember two of my bikes turning past 50,000 miles.

    In that time, I've scraped some paint and plastic, totaled a couple of bikes, and suffered a few serious injuries. Helmets saved me from grievous harm many times. One involved me being rear-ended at a traffic signal -- driver fell asleep at the wheel (~4:00 in the afternoon). I bounced and rolled over the car, landing on the ground behind the car. My bike didn't even fall over -- it was wedged in the front bumper. (Loved that bike, 1981 Honda CB750F. First brand new vehicle I ever purchased. It was also one of my 50k milers.) I was wearing a leather jacket, gloves, boots, jeans, and full-face helmet. Other than some general soreness, I was uninjured. Speed at impact was estimated at 30+ mph.

    Another major head impact occurred when a Corvette invaded my lane, attempting to avoid a car that turned left in front of it. I was already hard on the brakes, and would have missed the left-turning car. I don't know exactly what happened, but the side of my full-face Arai helmet cracked and had Corvette fiberglass embedded in it. I was unconscious for a few minutes, and suffered a dislocated shoulder, but no evidence of concussion or any other injury.

    Anecdotes aside, the classic "http://en.wikipedia.org/wiki/Hurt_Report" [Broken]:
    • "Safety helmet use caused no attenuation of critical traffic sounds, no limitation of pre-crash visual field, and no fatigue or loss of attention; no element of accident causation was related to helmet use"
    • "Helmeted riders and passengers showed significantly lower head and neck injury for all types of injury, at all levels of injury severity."
    -- Citations via Wikipedia, http://en.wikipedia.org/wiki/List_of_findings_in_the_Hurt_Report
    -- Full, original report http://isddc.dot.gov/OLPFiles/NHTSA/013695.pdf"

    Ranger Mike, you are certainly welcome to your choice of riding unprotected. However, I strongly disagree with your attempt to demean the proven safety record of helmet use.
    Last edited by a moderator: May 5, 2017
  17. Aug 1, 2011 #16


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    Saying "it's just made of foam" misses the considerable subtlety and engineering that goes into a bicycle helmet. Consider the thin outer plastic plastic. In cheap helmets this can be PET (similar to plastic bottles), while more expensive helmets have nearly indestructible polycarbonate (lexan), but in both cases this outside skin is tough (won't tear).
    Because it's thin it's also flexible, which is modified by bonding it to the foam. The assembly can't flex easily, which spreads the force of an impact over a wide area of foam, which then compresses and dissipates the worst of the collision energy. (This aspect is similar to that in bullet-proof glass.) The liner also compresses on the inside around your head, again spreading and reducing the force of impact on your skull. You might well imagine that the materials are selected carefully, however casual the helmet construction may appear.

    I have known two people who weren't wearing helmets and died from bike accidents (one wasn't even biking, he was just standing on his bike in his driveway when he fell and hit his head on the concrete.) On the other hand, my child and his playmate had a biking adventure. The friend lost control coming down a hill and came home with bruises and bloody road rash--and a dented and slightly cracked helmet. I have no doubt that helmet saved her life.

    So the magic is in the combination of compressible foam to provide cushioning and dissipate energy, a tough shell, the important bond between them that spreads the impact--and the engineering and testing behind them. It's not "just foam."
  18. Aug 1, 2011 #17


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    Your demonstration can last less than 10 seconds.
    - a hammer
    - a brick of foam

    Take the hammer, touch it to their skull (gently, it'll still make the point).
    Now, take the foam, insert it between hammer and skull.
    Ask them which they prefer.

    Quod erat demonstrandum
  19. Aug 2, 2011 #18

    Ranger Mike

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    pantaz i have no problem with non bias data collected in a fair impartial manner. i do take great pleasure pointing out erroneous data collected by insurance companies in an attempt to influence law makers to pass legislation that will benefit those insurance companies.
    One more thing...if you think adding five to ten pounds of weight to your head and having an impact will not effect your neck...try asking Dale E. who snapped his neck at Daytona. Next we will all have to wear HANS devices...no way buddies..you are entrenched in your beliefs and I in mine...let GOD sort it out after the crash!!!
  20. Aug 2, 2011 #19
    This is the same argument that 'seatbelts increase neck injuries'.

    A slightly curious line of argument because a HANS device would have probably saved his life.
  21. Aug 2, 2011 #20
    Two points.
    1.) The protection requirements (and logistics) for a driver of a 200mph+ race car are quite different than for a person riding a bicycle. The bicycle rider requires a light weight helmet that doesn't fatigue the neck. The race car driver is strapped into a seat and surrounded by roll bars and fire protection.

    2.) Didn't Dale E impact a wall head-on at a speed in excess of 100mph - and stop (all forward motion)?
  22. Aug 2, 2011 #21

    Ranger Mike

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    great points all, my friends...but on this subject I can not offer logical well thought out arguments and I lack critical thinking on this..lost too many bros to weird accidents that go counter to as these logical points..like racing..bike riding will subject you to some of the most off the wall scenarios possible...and friends died..nuff on this... so i sign off this post...

    ps did not mean to offend..just brought back old memories..
  23. Aug 2, 2011 #22
    Theres no offence to be had, it's a decent debate.

    I fully apprecitate the arguments made, it's just that rider/driver safety is something I feel there shouldn't be a compromise on.

    There obviously comes a point where extra gadgets and safety 'stuff' acutally decreases safety. I can understand the visibility argument becuase, visibility is something thats annoying me with modern cars, they've replaced the rear quarter window with crash structure. Keeps you really safe in a crash, but you can't see anything making a crash more likely.
  24. Aug 2, 2011 #23


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    Only when driving backwards... :wink:
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