Everybody knows that it’s easier to create a perfect, throwable (but non-lethal) snowball with snow that’s warmer and wetter – yet still below the freezing point. But why? The answer is in a thin liquid layer that’s found on every ice crystal, a phenomenon called surface melting, says Dr. John Wettlaufer, a Yale professor who’s written about the physics of premelted ice.
“At the surface of every ice crystal that’s a disordered layer, and as the temperature rises, there’s a greater anharmonicity in the amplification of surface molecules,” says Wettlaufer. Got it?
What Wettlaufer is trying to tell us is that at low temperatures – say ten degrees below zero – that little layer of liquid found in the snow crystals is very, very thin. When it’s warmer, the layer is thicker, so it’s easier to glue them together. ” When you’re making a snowball, you’re bringing ice with a watery surface together with ice with a watery surface. An intermolecular bond fuses the two together, ”he says.
The biggest takeaway here is that warmer winter days make for better snowball fights. If it’s zero Fahrenheit, its gonna take a lung time to build up your arsenal – unless you find a way to jump-start the snow melt (pre-melting snow inside isn’t cheating, right?).