Screaming gel balls reveal a way to power soft but noisy robots

A viral video of gel beads bouncing and squealing in

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a hot frying pan has led to the discovery that hydrogels slapping against a hot surface can generate substantial kinetic energy. This could one day give a power boost to bots made of such materials.

Scott Waitukaitis at the University of Leiden in the Netherlands was inspired by a YouTube video showing balls of water-saturated polyacrylimide gel shrieking when they hit the skillet’s hot surface, and leaping up and down as if the pan were a trampoline.

To find out why this was happening, Waitukaitis and his colleagues soaked hydrogel beads, often used in flower arranging, until they were about 99 per cent water by weight and dropped them onto pans heated to 215°C from heights ranging from a few hundred micrometres to 20 centimetres.

If the balls were dropped from less than 4 centimetres, they seemed to defy gravity by bouncing higher and higher with every leap until they reached that height, where they bounced stably for several minutes. Dropped from a greater altitude, they lost height with each bounce until they reached that sweet spot of 4 centimetres. 

Source https://www.newscientist.com/article/2141618-screaming-gel-balls-reveal-a-way-to-power-soft-but-noisy-robots/