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.

Read the article at Boston.com →