Surface tension.

Look, I get it. Most people don’t walk around thinking about surface tension. Yet it exists wherever there is a boundary condition. It enforces shape upon the world and is basically cool. I remember this little experiment we would do as kids, betting each other that we could make a steel needle float on water. Place a small strip of Kleenex in a bowl of water. On this floating piece of paper carefully place the needle. The paper soon saturates and falls away yet the needle continues to float all by its lonesome, held up by the force known as surface tension.

Raindrops on a leaf display this magic as well, as they form flattened spheroids held together by a kind of “skin”. They are flattened because of Earth’s gravity, otherwise they would form spheres. A very important question is whether the water droplets *roll* off the leaf or *slide* off the leaf. You will be happy to know that they in fact *roll*. Those of you in the “slide” camp will just have to plot your revenge. By the way I note in passing that WaterSkins would be a good name for a rock band.

And life itself has found a way, he says, stealing a line from Jurassic Park. Insects called water-striders glide across the surface of streams and lakes, quite literally walking on water. The pads on their legs and feet are perfectly shaped to balance their weight with the force of surface tension. They clearly read ahead in their physics textbook and anticipated the ol’ floating needle trick. I can imagine an awful lot of water-striders met a watery fate until those smart folks back in the evolution lab came up with the perfect foot design.

Call it “surface intention”. Heh.