A Prince Rupert's Drop Is Both Extremely Fragile And Virtually Unbreakable
Would you believe that there's an object that's both nearly unbreakable and so fragile it shatters instantly? Well, believe it. This paradoxical object is a piece of glass known as a Prince Rupert's drop.
Wait...What Is It, Exactly?
Despite its seemingly impossible characteristics, a Prince Rupert's drop is surprisingly simple to make: you just drip molten glass into super cold water. What results is a teardrop-shaped piece of glass that's nearly impossible to break at one end, and incredibly fragile at the other. In the words of the Royal Society of London: "The head withstands hammering on an anvil, or...squeezing in a vice, indenting its steel jaws, without fracture; yet breaking the tail with finger pressure caused the whole to explode into powder."
Why is it named after some guy named Rupert? It's said that Prince Rupert, the nephew of King Charles I, was the first to bring the glass oddities to England in 1660. They had been around long before then, however, possibly dating back to Roman times.
How Is This Possible?
Here's how: when the glass hits the water, the outside layers cool very quickly while the inside remains molten. The effect of thermal expansion makes liquids expand when they're hot and contract as they cool. That means that the molten interior is trying to expand at the same time as the cool outer layer is contracting inward. As the whole thing crystallizes, these equal pushing and pulling forces build up in one long chain that stretches from the head of the drop to the tail. Once the drop is cool, it's locked into this state of high tension. The Royal Society compared it to an arch: in one piece, it's incredibly strong, but if any part of it is broken, the whole thing fails. In the case of a Prince Rupert's drop, it fails spectacularly, in an explosion of fine glass shards that must be seen on a slow-mo camera to be believed. Luckily, you can do just that in the video below.