Thanks to a strange phenomenon known as the Leidenfrost Effect.
The Leidenfrost Effect, first described by Johann Gottlob Leidenfrost in 1756, is a phenomenon where liquid appears to levitate on a surface. While it is not really levitating, it is still really cool to see. You may have already experienced this effect unintentionally while cooking.
The science behind this effect is really simple: If you put water on a hot surface that is below its boiling point, 212 degrees Fahrenheit, the water will bubble and evaporate. However, if you heat the surface way beyond water’s boiling point, the Leidenfrost Effect can occur. If the temperature of the surface is really, really hot, a thin layer of vapor will form between the surface and the water, and this vapor insulates the water and slows the evaporation process. This layer of vapor makes the water droplets appear to levitate.
And this effect works for any liquid.
Alex Grounds and Richard Still from Bath University studied the Leidenfrost Effect and how water drops traveled on different textured surfaces of different temperatures. They found that water can move in different directions, even uphill, depending on the temperature of the textured surfaces. They even discovered that the droplets can climb really steep inclines by increasing the sharpness of the “teeth” of the surface. Keeping these results in mind, they created the Leidenfrost Maze.
The idea behind the maze was to guide the water droplets by arranging grooved hotplates. ‘We think the droplets change direction depending on how fast the gas evaporates from the surface of the droplet and how much the droplet is levitating, combined with the effect of the textured surface that allows it to be propelled along and even go uphill,’ said researcher Alex Grounds.
This short four minute video explains the Leidenfrost Effect, and shows water droplets making their way through the maze.