No One Is Quite Sure Why Ice Is Slippery
Thay intuited that molecules near the surface behave differently from those deep within the ice. Ice is a crystal, wich means each water molecule is locked into a periodic lattice. Though,at the surface,the water molecules have fewer neighbors to bond with adn thus have more freedom of movement than in solid ice.In that so-called premelted layer, molecules are easily displaced by a skate, a ski, or a shoe.
Today, scientists generally agree that the premelted layer exists, at least close to the melting point, but they disagree on it’s role in ice’s slipperiness.
A few years ago, Luis MacDowell, a physicist at the Complutense University of Madrid, and his collaborators ran a series of simulations to establish which of the three hypotheses—pressure, friction, or premelting—best explains the slipperiness of ice. “In computer simulations, you can see the atoms move,” he said—something that isn’t feasible in real experiments. “And you can actually look at the neighbors of those atoms” to see whether they are periodically spaced, like in a solid, or disordered, like in a liquid.
They observed that their simulated block of ice was indeed coated with a liquidlike layer just a few molecules thick, as the premelting theory predicts.When they simulated a heavy object sliding on the ice’s surface, the layer thickened, in agreement with the pressure theory. they explored frictional heating.Near ice’s melting point, the premelted layer was already thick, so frictional heating didn’t considerably impact it.At lower temperatures,however,the sliding object produced heat that melted the ice and thickened the layer.
“Our message is: All three controversial hypotheses operate simultaneously to one or the other degree,” MacDowell said.
Hypothesis 4: Amorphization
Or perhaps the melting of the surface isn’t the main cause of ice’s slipperiness.
Recently, a team of re