Free Never Mind the Bullocks, Here's the Science by Karl Kruszelnicki Page A

a preliminary study, rather than a fully developed work.
    He started thinking about scalp hair, which is a collection of about 100,000 individual shafts. He thought that perhaps it might be possible to model this complex system of 100,000 separate units in a simple way.
    Even today, there is still no single widely accepted model that predicts how hair will behave. And there is so much that we still do not know about ‘tangles’—e.g. how they form, how they resolve, why they form here rather than there, and why there are sometimes so few or so many.
    Hair Tangles—Theory
    He developed a theory of geometric modelling of hair, setting up a simple model based on the science of polymer dynamics.
    He made a few assumptions. First, he modelled straight hair (or a bunch of straight hairs) as a rigid segment with a known length. Curly hair was modelled as having a straight section and a wavy section. Second, he assumed that these hair strands are fixed into the scalp at one end but point in all possible directions at the other end. A hair can also change from pointing in one direction to pointing in any other direction. And, third, he assumed that any two hairs, or any two groups of hairs, can cross each other, and they can do so at a variety of angles.
    There were other assumptions as well. The hairs are also subject to random turbulence. They can move independently of each other. But occasionally they can also move in a coordinated motion—as in the ads on TV, when the female model’s metre-long hair falls like a slow-motion wave.
    The hair product industry has its special language to describe hair—but so does science. ‘Oily’ made the physicist think of ‘cluster formation and binding energy’, while ‘straight and curly’ started him ruminating on ‘general geometry and spatial organisation’. ‘Thin and thick’ was more than just a description of diameter—to a physicist, it was ‘the influence of elementary characteristic properties on general behaviour’.
    His theory predicted that straight hair should have more tangles than curly hair. This is the opposite of what you would expect.
    Bad Hair Day

Human beings are basically hairless apes with big brains.
    Hair Tangles—Experiment
    Theory is one thing, but experiment is another.
    His experiment involved two hairdressers checking for tangles in the hair of their clients, for three weeks. They checked 212 people (123 with straight hair, and 89 with curly hair) in the late afternoon between 4 and 7 pm. This time was specifically chosen to allow the maximum time and opportunity for the hair to tangle after a hard day of waving about in the breeze and rubbing against the trees.
    In science, you need definitions. Therefore, a ‘tangle’ was defined as a ‘cluster or grouping of hairs that resist combing’. This excluded natural clusters of hair, such as a curl or a ringlet. To find any tangles, the hairdressers used a comb with a 3 mm separation of the teeth.
    The experimental results were astonishing—on average, 5.3 tangles were found in each head of straight hair, but only 2.9 for curly hair.
    At this stage, we still don’t fully understand what is going on.
    Why More Tangles with Straight Hair?
    The initial theory implies that the shafts of straight hair cross each other less often than do the shafts of curly hair. Now this is reasonable, because you would think that the straight hairs would tend to stay parallel to each other, and not cross each other.
    But the physicist’s theory also told him that when the straight shafts do cross, they do so at a greater angle than for curly hair. Perhaps this is the clue—the critical factor. Human hair does not have a perfectly smooth surface. A microscope shows that the surface is coated with fish-like overlapping ‘scales’ with shallow notches.
    Perhaps these scales ‘lock’ into each other only when the hair shafts cross each other at a large angle?
    Perhaps the individual strands in curly hair tend to