• Question: how many newtons does it take to break human bones?

    Asked by 876nepk42 to Ed, Kerrianne, Nina, Oli, yoyehudi on 7 Nov 2017.
    • Photo: Kerrianne Harrington

      Kerrianne Harrington answered on 7 Nov 2017:

      Good (and sort of alarming) question! I have to say I don’t know myself, and I’d rather not do an experiment to find out! We know that it must be more than what are bones have to deal with carrying ourselves around, and that there will be some variance from person to person because of different health conditions and builds that would affect bone density. From the way that people break their bones, I also wouldn’t be surprised if it also depends on what direction the force is applied. I’ve seen lots of surprising breakages from people skating and falling on their ankle at a funny ankle! I’m not really sure, and I don’t know if I’m entirely convinced by numbers I see online.

    • Photo: Oli Wilson

      Oli Wilson answered on 7 Nov 2017:

      I found an old paper from 1959 that suggested the human femur (in our upper leg, the longest bone in our bodies) can will break when squashed with 20,000 pounds per square inch of force. Those units are pretty old-school though! If the middle of the femur’s shaft is about one square inch in cross-sectional area (seems about right?) then it will break under 20,000 lb of compression – that’s around 89,000 Newtons and very approximately one and a bit elephants. Good work our bones!
      Kerrianne’s spot on about the variation too, though. You can see the effects of force coming from different directions in this video http://www.bbc.co.uk/programmes/p01s93jc – leg bones are designed to be squashed vertically, not pulled, twisted, or bent in the middle. That’s why you’re more likely to break your leg in a bad football tackle than by jumping up and down.

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