Liquid Film Motors Finally Explained

Last year, a group of Iranian physicists made the extraordinary discovery that motors can be made of nothing more than a thin film of water sitting in a cell bathed in two perpendicular electric fields. The unexpected result of this set up is that the water begins to rotate. Divide the water into smaller cells and each rotates too. The team at the Sharif University of Technology in Tehran have a number of fascinating videos of it in action. They raise an interesting question: the electric fields are static, so what’s making the water move? Now Vlad Vladimirov at York University in the UK and a couple of droogs from Russia have delved into the hydrodynamics to work out what’s putting the oomph in this motor. The key turns out to be the scale on which the effect takes place