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Which is stronger?

  1. Jul 5, 2013 #1
    Which is stronger, a rope made of 100,000 hairs or a same-sized giant single hair? I know this question might be a bit ridiculous but I really wanna know. I think the rope of 100,000 hairs is stronger.
  2. jcsd
  3. Jul 5, 2013 #2
    Yes because if 1 hair breaks, it does harms the others but when there is a small cut or some defect in the large one, it may stretch and get bigger and bigger resulting in breaking of the giant hair.
  4. Jul 5, 2013 #3
    Do you mean it doesn't harms the other hairs? Or what.
  5. Jul 5, 2013 #4

    In general, stranded wire versus solid wire comes down to a question of flexibility versus strength. Because the individual strands of a wire are more flexible, stranded wire can be bent and twisted more easily where solid-core wire would develop metal fatigue and eventually break. On the other hand, solid core wire is stronger than stranded wire, so any applications in which strength is important call for solid wiring.

    Read more: http://www.ehow.com/info_8223598_difference-stranded-wire-solid-wire.html#ixzz2YADHDNEx
  6. Jul 5, 2013 #5
    So the rope of 100,000 hairs is stronger than a same-sized giant single hair, isn't it?
  7. Jul 5, 2013 #6
    Not according to that link. "Stranded" is equivalent to your 10,000 hairs, and they are saying that the solid wire is stronger than the stranded wire. That is only one reference, though, and it relates to wire, not string.
  8. Jul 5, 2013 #7
    Hmm. But this link say the other thing http://www-materials.eng.cam.ac.uk/mpsite/short/OCR/ropes/
  9. Jul 5, 2013 #8
    Depends on how you envision the structure of the giant size hair. A hair does not have a uniform composition, it consists of coaxial layers of different strength. So is reasonable to assume that surface forces contribute significantly to the strength of the hair.

    Thus if you increase the size of the hair, its strength should partly proportional to its radius, and partially proportional to its cross section area (i.e. radius squared).

    However, by bundling several hairs together you will get a much larger surface increase, so if surface forces are dominant, this will be stronger.
  10. Jul 5, 2013 #9
    So, I think the definite answer is the rope of hairs is stronger than a same sized single giant hair based on your given answer.
  11. Jul 8, 2013 #10
    It's not a ridiculous question. Not thinking about it has caused death and destruction throughout history, such as the failure of the Malpasset Dam for example.

    Smaller fibers are usually stronger than larger ones due to, among other things, defects. If a large piece of glass has a small crack, for example, then that's a stress concentration and can lead to premature failure. And it's hard to make a large piece of glass without any defects. However, if a small fiber of glass has a defect, then chances are that it has already broken. A small fiber of glass is therefore much closer to its theoretical strength than a large fiber. This is why the incredible strength of fiberglass.

    The same principle applies to hairs and metals, although to varying effect.

    On the other hand, if you bundle a bunch of hairs together then you will inevitably end up with empty space between the fibers. That empty space reduces the strength of the overall structure compared to having one large fiber. So ultimately which one is stronger depends based on several factors. Shooting from the hip, I'd probably prefer 100,000 hairs over one single large one....coated with some type of protection, of course.
  12. Jul 8, 2013 #11


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    @ Mohd Abdullah
    The answer to this question depends upon the level at which you want to appreciate the problem. If you just consider the ideal case, then the modulus of the material is the same, however you use it. (The simple Maths will give the same answer for a given total cross sectional area and it's the answer you start off with when trying to come to a ball-park figure.) The practical answer is, of course, that many strands would be effectively stronger. Although using a hair as the example for this question is not really fair, as the hair is already a composite. It would be better to consider steel wires as an example - but even then, the mixture of atoms in steel will affect the result for very thin wires in the order of molecular thickness.
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