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WATCH: What Happens When a Bullet Hits an 'Unbreakable' Prince Rupert's Drop

One of science's weirdest enigmas just got freakier.

FIONA MACDONALD
30 DEC 2016
 

For those of you who aren't familiar with the Prince Rupert's drop, this weird, scientific enigma is a glass object that's created by dripping molten glass into very cold water.

 

That process creates all kinds of crazy physical properties, which we'll go into later, but the end result is a teardrop-shaped piece of glass that's pretty much unbreakable at its bulbous 'drop' end, but which shatters from the slightest pressure at the elongated tail end. Scientists have been obsessed with them since the 1600s. But what happens if you shoot one with a bullet?

In his latest video, Destin from Smarter Every Day uses the newest technology to find out - and he's documented the entire thing at a glorious 150,000 frames per second.

Spoiler: Prince Rupert's Drops are so strong, they actually cause a bullet to shatter. And it's incredible science:

So what's going on here? As you can see in the video above, shooting the Prince Rupert's drop sometimes causes the object to shatter, but that's not because it's breaking the glass at the thick end. 

In glorious slow motion, you can watch as the bullet bounces right off the wide end of the drop, sending out shock waves that then rattle the rest of the structure and cause the thin end to break, resulting in the entire thing exploding. 

 

To understand how this works, you first need to understand why a Prince Rupert's drop is so weird in the first place.

When the Prince Rupert's drop is made, molten glass is poured into extremely cold water, causing the outside of the drop to cool and solidify almost instantly, while the inside remains molten and cools more slowly.

Because of thermal expansion, glass wants to expand while it's hot, and contract while it's cool. 

That means that as the molten inside of the glass gradually cools down, it wants to contract and pull the solid outer layer inwards. But because the outer layer is already solidified, this just makes the whole thing tighter, making that bulbous end of the Prince Rupert's drop pretty much indestructible, and, as we now know, bullet-proof.

But because the outside of the glass is in extremely high compressive stress, and the inside is in extremely high tensile stress, if one link is ever broken, then the whole thing explodes, feeding off its stored internal energy.

This is what happens when the fragile thin end at the back of the drop gets broken - it releases all that pent-up energy and causes the whole thing to shatter. 

To understand that properly, check out this incredible slow-mo video that Destin originally did on the Prince Rupert's drop a few years ago:

Now we know that these incredible pieces of glass are even more fascinating, because they can also withstand a bullet from a .22 rifle when they're shot at the right angle.

In fact, if you watch to the end, you'll see that a small Prince Rupert's drop is so strong it actually makes a bullet shatter. Check it out in the video above, and marvel once more at the beautiful mystery that is science. 

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