Swimming on the Nanoscale
Ordinarily, small things must expend a lot of energy to swim. At small length scales, the the ratio of inertial to viscous forces (the Reynolds number) decreases, and friction becomes a big problem for small swimmers. If you were the size of a bacterium, moving through a fluid would feel more like burrowing than swimming.
This problem is the bane of anyone wanting to build tiny swimming robots. But now, as reported by PhysOrg, a team of scientists has devised an ingenious way to turn this bane into a boon by having a micro-robot “treadmill” across the surface. The robot would roll across the fluid surface in the same way that a tank rolls across solid ground; what is marvelous is that this works precisely because the viscous forces are so large on this length scale that the fluid surface is, in effect, solid. The analysis shows that this method of locomotion loses very little energy to friction.
This idea seems obvious in retrospect, but there are a lot of smart people who didn’t think of it first. In any case, it’s a really beautiful solution.
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