Something incredible happens when you smash this glass bulb with a hammer

SmarterEveryDay

This teardrop-shaped object, called a Prince Rupert's Drop, is a paradox wrapped in a glass structure.

It's created simply by plunging molten glass into cold water. 

But this reaction imbues the glass with some pretty amazing properties. Take a crack at hammering the head and it is nearly impossible to break.

But just slightly tweak its tail and the whole thing bursts into a glittery spray of exploded glass.

YouTube/SmarterEveryDay

But why?

The answer lies in its internal balancing act of compressive and tensile stresses. After the glass is dropped into the water, the outside layer of glass cools while the inside stays relatively hot. The outer layer of glass shrinks as it cools and forms a solid shape.

When the glass core of the drop eventually cools, the molecules inside have no where to shrink to because the outer layer is already set, so they pull toward each other, creating a super high tension inside the bulb, which eventually hardens. This tension is released when the tail is even slightly tweaked, it releases a cascade of energy that propagates the entirety of the tail and bulb, exploding it outward. 

Check out the whole video posted on YouTube by SmarterEveryDay for more awesome shots of glass breaking in slow motion.