Did you guys ever hear about Prince Rupert’s Drop? The British Royal Society was really interested in these things back in the 1600s.
It’s basically a long, thin, practically snaky bit of glass that you get when you drop some molten glass into water. It solidifies into a shape like this:
The interesting and weird thing is, you can’t really break the bulb part. You can take a hammer to it but it won’t break. But the long tail is fragile and easily broken. And if you break any part of this thing, it explodes. Really, it just blows up into a million tiny little shards.
With modern high-speed cameras, they’ve managed to measure the speed of the fracture at slightly faster than one mile per second.
The reason why it breaks like this is because, when the molten glass rapidly cools, the surface hardens right up, but the inside still stays hot for a while. As the inside cools, it pulls in on itself really hard in all directions, leaving the entire drop in a constant state of high tension. When it’s entirely cooled, it only takes a tiny fracture to release that chain reaction of released tension that breaks all of it almost at once.
Somewhere on the internet there’s high speed video of somebody shooting Prince Rupert drops with a rifle.
You actually see bits fly off of the head, but it doesn’t break… but the impact cracks the tail and that sets it off.
Incidentally, the same basic thing is what’s going on with tempered glass, in a much less dramatic way.
Shieldfoss 