So what do a human hair, a steel pipeline and an amoeba’s flagella have in common? Once they all assume the right proportions, they all work the same. A miles-long pipeline, though it can be massively thick when looked at up close, looks like a long, spindly hair when it’s spread across the landscape. When a hair is short enough (like a military buzz cut) it’s sticking out from the head directly as it grows. It’s short enough that its internal strength can stand up to the force of gravity. As it grows, however, it has to ‘carry’ a longer length, and gravity pulls it down.
Even those of us who aren’t at MIT — or working for Pixar — can see the interplay of gravity, exerting a force in in one direction, and the structure of the actual ‘hair’ curling in on itself. Grow a hair long enough, and its own weight will pull it straight. However, as you get to the very tips of the hair, which don’t have as much weight on them, the curl will come back. The more towards the end you get, the less weight is on it, and the more extreme the curl.
You can see this successfully rendered in the table scene above. Although it’s clear that the young boys have larger, softer curls than the girl, the hair on the top of their heads is piled up, while hers is pulled straighter than the rest of her hair. The weight is pulling the top of her hair straight while the bottom is in tighter ringlets. In real life, people will notice that their ‘straight’ hair will curl at the end, showing that what they have is curly hair that only has enough strength to curl at places that don’t support a lot of weight. Meanwhile, in the macro scale, an oil pipeline will ‘curl’ in reverse. Its length it set out horizontally, so gravity ‘pulls’ its straight structure into a curl. Shifting earth or driving wind can cause it to curl in on itself, at exactly the point that are feeling the most force. The ends, or the parts that are supported by struts, will remain. A straight pipeline is, essentially, a curly hair in reverse, but the interplay of forces is the same.