• Question: how much preasure can the arms take for an average 12 year old boy

    Asked by garagod2 to Helen, Jenni, Mark, Martin, Stu on 20 Jun 2011.
    • Photo: Jenni Tilley

      Jenni Tilley answered on 20 Jun 2011:

      Pressure or force?

      We can do a quick back of the envelope estimate…

      Bone has a maximum strength of about 130MPa – tha means it can carry 130,000,000 newtons per metre squared of bone.

      If your arm has a radius of about 5cm (or 0.05m), and assuming your arm bone is solid and not jointed, there is (pi x 0.05 x 0.05) metres squared of material available for carry the load. That’s about 0.008 metres squared.

      SO you’re arm can carry (130,000,000 x 0.008) newtons which is about 975,000Newtons.

      Since 10newtons= 1kg, it would take 97,500Kg to break your arm…

      But we did make some big assumptions – you’re bone is actually hollow and it is jointed. Plus your tendons adn ligaments are not as strong as your bone. So I definately wouldn’t try this at home!

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