A RECORD-BREAKING cold front moved through the country last week, and here’s one surprising consequence of the ultra-low temperatures some regions experienced: It’s nearly impossible under those conditions to make a snowball.
In a post on the “physics of a snowball” on Northeastern University’s research blog, 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 in extreme cold.
When you pack together snow, he explains, the pressure you apply actually causes some of the snowflakes to melt. (Unlike most materials, water liquefies under pressure.) Then, once the pressure’s off, the liquefied snow refreezes in its new, hopefully spherical state. But when it’s really cold outside, 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.