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Funny question

  1. Nov 23, 2008 #1
    This isn't a homework question, just a random question. The other day I hit my head really hard on the ground and ended up getting a concussion. The athletic trainer at my school said that if I would have hit my head on a pad, I would not have received a concussion. Why is this?

    Besides the obvious answer that the pad is softer. I mean, does the pad make that much of a difference?
  2. jcsd
  3. Nov 23, 2008 #2


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    Yes it does.
    When you hit something soft, your exposed part of your body decelerates at a lower rate than if you hit a solid ground. The difference is that the brain doesn't get an acceleration as big as if you hit a solid ground. A greater acceleration of the brain makes it hits the skull faster (so stronger) so it really makes a difference.
  4. Nov 23, 2008 #3


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    The time allowed for acclerating is longer if the pad is hit than if something with a high elasticity is hit, then the force would be less because force is change in momentum relative to change in time.
    Are you all right?
    Last edited: Nov 23, 2008
  5. Nov 23, 2008 #4


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    Per Newton's 2nd law, Impulse = Change in Momentum, that is [tex]F\Delta t = m\Delta v)[/tex], which is to say, the force on your head, F is [tex] F = m\Delta v/\Delta t[/tex]. So since you would hit the pad or ground at the same speed, it's the time, t, that lessens the force on your head using the soft pad, because it takes a longer time and a longer distance for your head to come to a stop.
  6. Nov 23, 2008 #5
    Wow, I didn't know a small pad would make that big of difference. Thanks!

    Yeah, I'm okay. I actually got lucky, I didn't get that bad of a concussion. Lol.
  7. Nov 24, 2008 #6
    That's why hammers are made of steel rather than sponge-rubber. Or, why you may use a rubber mallet instead of a steel hammer if you're trying to be more gentle.
  8. Nov 24, 2008 #7
    Closely related to the FT = mv argument described above is that fact that if your head and the object it hit were completely incompressible, the time of impact would approach zero ....to stop your hard head....so for FT to equal mv, F would have to approach infinity..or at least be HUGE!!!!...

    A related effect is based on pressure as force per unit area....if you can spread out the area of impact you can reduce the force on an individual part of your noggin...think of a football helmet, for example....the impact of a sharp knee, for example, is spread by the hard exterior over maybe a quarter of the helmet area on the side of impact....so both the force on an area as well as the time of impact are changed to your benefit...

    PS: don't let girls push you around that way!!!
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