A record-breaking cold front is moving through the center of the country and here’s one surprising consequence of temperatures as low as minus-fifty: It’s nearly impossible under those conditions to make a snowball. This is according to a fun post on the “physics of a snowball” that ran last week on the Northeastern University research blog. There, J. Murray Gibson, dean of the university’s College of Science, explained that snowball formation depends on a degree of melting that’s hard to achieve when it’s really cold outside.
When you pack together snow, the pressure you apply actually causes some of the snowflakes to melt. Then, once the pressure’s off, the liquefied snow refreezes in its new, more compact (hopefully spherical) state. The article adds that water liquefies under pressure because, unlike any other commonly available material on earth, it’s denser in liquid form than solid form, which is why Cokes burst in the freezer, and no matter how much pressure you apply to a tree, it’s not going to turn into a puddle.
When it’s really cold outside, though, the amount of pressure you need to apply to snow to make it melt, and thus stick together as a snowball, is beyond the capacity of most human hands. So, there will likely be no snowballs in Eau Claire today, not that anyone there is likely to want to go outside anyway.