Why water levitates on a hot surface

The Leidenfrost effect can make beads of liquid float above a hot surface.

Why does water skitter across a hotplate in tiny droplets? You’d expect water exposed to a boiling-hot surface to evaporate quickly and disappear in a puff of steam – but this is not the case.

The behaviour is due to a phenomenon known as the Leidenfrost effect, after the 18th-century German doctor who first described it. The bottom layer of the droplet that touches the hot surface does indeed evaporate, but the it forms a thin cushion of vapour that temporarily protects the rest of the droplet from the extreme heat.

This keeps the rest from becoming vapour and lets the droplet move around the hot plate with ease.

As the video above shows, that’s just the start of the things that the Leidenfrost effect is good for.

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