I can walk on water, so can you

This week was the 2013 IgNobel prize ceremony, the IgNobel prizes are the Nobel prizes’ amusing little brother. The Physics IgNobel was won by a bunch of Italian physicists walking on water. Presumably due to their limited budget, they did this on Earth, but rigged up a harness to take 5/6ths of their weight, to simulate walking on water on the Moon where gravity is only 1/6th as strong on Earth. They concluded that due to this weaker gravity, if you wore flippers and got a move on, it might just be possible to walk (briskly) on water. This may be might marginal, but if we looked further afar, say to Saturn’s moon Tethys, then with gravity only about 1.5% that on Earth, we should all be able to walk on water.

The physics behind this is that the surface of water is effectively under tension (a contracting force), and so resists deformation. This enables small insects called pond skaters (also called water striders) to stand and walk on them on Earth. I’ll be teaching this to third year students in a few weeks in the soft matter and biological physics module I co-teach. I wrote a blog post on this a year ago.

Small insects are very light, the force of gravity is weak and so standing or walking on water is easy. Bigger animals are much heavier and so the force of gravity on them is to large for them to stand on water. But although they cannot stand on water, some smallish lizards can run on water. The classic example is the basilisk lizard, also known as the Jesus lizard, for reasons that will be obvious if you watch this:

It can literally run on water, basically by trapping air pockets beneath its rear feet and running so fast that it has moved on before the pockets have time to collapse. These lizards have a mass of bit less than 100 g. This year’s Physics IgNobel have shown, that with a bit of training and flippers on our feet we might be to to do the same, but only on the Moon. Truly, this would be “That’s one small step for a man, one giant leap for mankind.”