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.

Read the article at The Boston Globe →