Watch Liquid Nitrogen White Walkerize a Watermelon
Have you ever seen someone shatter a combination lock with a hammer? Well, now you can, courtesy of 20 gallons of liquid nitrogen and the unbridled curiosity of WIRED staffers. The ultra-cold fluid is usually used for fancy cooking, wart removal, and fogging up nightclubs. But today you can watch how different objects respond to a whacking after taking the polar plunge—in slow motion.
Spoiler: There’s lots of shattering. Almost anything has the ability to crack apart in a spectacular explosion—even a peacock feather, or a baseball—if you leave it in liquid nitrogen long enough. Just how long depends on how quickly heat moves through the material. Scientists call this rate thermal conductivity, and it’s not as complicated as you think.
Imagine you’re holding a Styrofoam cup in one hand and a metal mug in the other, and then someone pours piping hot coffee in both. You’ll probably drop that metal mug real quick, because it’s a great thermal conductor and heat travels through it immediately. On the other hand, your Styrofoam cup is a bad thermal conductor and will spread the coffee’s heat much more slowly. (Yay for your hand!)
“A baseball is more like the Styrofoam cup,” says Stanford biophysicist Michael Fayer. They’re well insulated, full of air and dry material. “It’s slow for the inside to get cold, so only the surface might cool.” To make a baseball shatter, you’d have to leave it in liquid nitrogen for a lot longer than, say, a rose, which is full of water molecules. (Water forms little crystals when it freezes, making a structure rigid and breakable.)
A cold, rigid object is no friend of the sledgehammer. When molecules are cooled down, they get slower and closer together. So when you whack them, they aren’t able to spread out the stress of the impact because they can’t move around each other. Instead, the impact points trigger a fracture, and the object soon becomes many smaller objects.
Metals, on the other hand, completely change their atomic structure when they’re exposed to different temperatures. When a metal is hot, the atoms are super mobile, poised and ready to mend a blow to their crystal lattice structure. To the naked eye, this reparative behavior looks like bending. Cool a metal down, however, and those once-speed demon atoms aren’t quick enough to repair breaks, making the structure brittle. And remember, metals are really good thermal conductors: Dunk a piece of metal in a vat of -320° F liquid nitrogen, and it’ll look like it crossed a White Walker.
The same thing will happen to any object if it’s submerged in liquid nitrogen long enough, regardless of how good it is at thermal conducting. But it’s probably best to leave those experiments to T-1000.