Q & A

Warm, wet key to ice being sticky

A warm, damp tongue may stick to ice as the warmth temporarily melts ice at its surface. The water quickly refreezes and creates an icy link.
A warm, damp tongue may stick to ice as the warmth temporarily melts ice at its surface. The water quickly refreezes and creates an icy link.ST FILE PHOTO

Q Why is ice sticky?

A Ice is sticky, but only to certain kinds of surfaces at certain temperatures. What really happens is that conditions are just right for a shared ice layer to form between the two surfaces and link them.

A warm, damp tongue or slightly sweaty finger may stick readily to an ice cube as the warmth temporarily melts ice at its surface. Once the warmth has dissipated, the water quickly refreezes, creating an icy link. If a cold, dry object touches the same ice cube, there is no melting and no adhesion.

Most of the time, however, ice is slippery, as ice skaters and Antarctic penguins demonstrate. The slipperiness of ice has a more complex explanation or combination of explanations.

It was long believed that pressure melting and frictional heating in some combination released liquid water at the surface of the ice so that sharp or even smooth objects could glide across.

More recent research has also focused on the idea that a permanent liquid-like layer lies atop the ice, even at temperatures far below the freezing point.

And a 2014 research published in the journal PCCP, Physical Chemistry Chemical Physics, suggests that a common supersolid skin, both elastic and temperature-stable, covers both water and ice, and is responsible for its slipperiness.

NYTIMES

A version of this article appeared in the print edition of The Straits Times on July 14, 2017, with the headline 'Warm, wet key to ice being sticky'. Print Edition | Subscribe