For athletes, the Winter Olympics mark the culmination of a grueling four-year pursuit of gold, silver or bronze that demands time commitments and physical sacrifices inconceivable to most.

For viewers, they’re a source of entertainment, national pride, and often-obscure stories thrust into a global spotlight that shines for two weeks.

But for the University of Nebraska–Lincoln’s Tim Gay and his fellow physicists, the Winter Olympics are a masterclass in classroom physics applied on ice and snow. Though he’s best known for explaining the Newtonian physics at play on the gridiron, Gay recently helped Nebraska Today understand a few of the phenomena behind (and underneath and around) the athletic feats of the 2022 Winter Games.

Slip ’n slide

Most events at the Winter Olympics, whether figure skating or hockey or bobsledding, are defined by speed. (Apologies to curling.) On a basic level, viewers understand that those sports owe their speed to the fact that they take place on ice.

On a similarly basic level, physicists have long understood that ice lends itself to speed because it’s slippery — and that it’s slippery because its surface includes an ultra-thin layer of water that reduces friction between it and whatever sits atop it. But if the temperature is low enough for the underlying water to freeze into ice, why does the surface layer escape the same fate?

For roughly a century, many physicists thought that the pressure of, say, a skate blade or bobsled runner was enough to melt the surface, producing a layer of water over which the blade or runner could then glide. Eventually, though, experiments and math refuted the idea. Later, physicists proposed that the friction between a moving object and the ice beneath it would generate enough heat to yield a veneer of water. But that explanation couldn’t account for a fundamental, intuitive fact: Ice is slippery even when simply standing on it, totally motionless.

So, in the 1950s, physicists circled back to an explanation that the legendary physicist Michael Faraday had forwarded a century earlier: that solid ice inherently features a thin liquid layer on its surface. And over the past 70 years, experiments and simulations have come to support the idea that this thin layer is actually due to its molecular structure.

The water molecules of solid ice are arranged in a static, crystalline structure that locks into place thanks to strong bonding among the molecules’ hydrogen atoms. At the surface, though, the top molecular layer has nothing further to bond to. The weakening of their bonds allows those top molecules to begin vibrating more than the ones below, ultimately returning them to an amorphous state — either water or possibly loose “molecular marbles” on which Olympic athletes speed their way to glory.

“This thin layer is what makes ice slick,” Gay said, “and makes the Olympics so fun to watch.”