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By Hamish Johnston
In this fantastic video, physics students at the University of Bath in the UK have had some fun with the Leidenfrost effect. This occurs when a liquid drop comes in contact with a hot surface that produces an insulating layer of vapour that keeps the drop from evaporating rapidly. This layer also allows the drop to glide effortlessly over the surface – and that’s where the fun begins.
It turns out that if you replace a smooth surface with the sort of asymmetrical teeth found in a ratchet, the drop will move rapidly in one direction. By using ratchet surfaces to accelerate liquid drops, the team has made the drops move uphill and even follow a predetermined path through a maze.
And if you wonder what would happen if you combined the Leidenfrost effect with the paramagnetic response of a liquid, check out the beautiful image in the article “Levitating drops controlled by fridge magnets”.
Nice work, but simple to understand. It works just in the opposite way the gravity works for an object on a inclined plane. Due to the component of the gravitational acceleration g determined by the inclination-angle of the plane, the object feels a force downwards along the plane. In the case of the Leidenfrost effect, the Leidenforce force points upwards and on a toothed inclined surface, its componemt pushes the drop up the inclined toohed surface and it moves from one tooth to the other. On a perfectly flat suface, the drop will only sizzle and dance up and down.
Acts magnetic.
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Some very nice work there, partly lab, partly educational. I think that such demonstrations, related to the “bangs-and-smells” that originally seduced many eventually serious scientists into their professions, are much neglected, educationally speaking.
The dumbed-down sound-bites and clowning currently dominating so-called TV-science programmes are intellectually sterile or misleading, and have little or no lasting educational benefit, whereas counter-intuitive, intellectually stimulating effects with genuine introductions to explanatory descriptions can attract the really bright minds and hook them. Other minds don’t matter so much, though every bit of education might help to create a functionally less-benighted public.
In short, to neglect or distort such material might indulge advertising sponsors, but for the rest amounts to betrayal of individuals and of society at large.