spaceSpace and Physics

Watch What Happens When You Shoot An “Unbreakable” Prince Rupert’s Drop With A Bullet


Katy Evans

Katy is Managing Editor at IFLScience where she oversees editorial content from News articles to Features, and even occasionally writes some.

Managing Editor

Will it break? SmarterEvertDay/YouTube

What’s a Prince Rupert’s drop, you ask? Well, science lovers, read on.

A Prince Rupert’s drop is what happens when you drop molten glass into very cold water. The glass cools into a tadpole-shaped teardrop with a bulbous, “unbreakable” drop and a fragile tail that will shatter at the slightest sign of stress.


They have been fascinating scientists since the 1600s, who have been testing the properties of these drops and just what they can withstand for centuries. Luckily, scientists and generally curious truth-seekers these days have YouTube channels where they perform their experiments so we can watch and, of course, observe the results.

YouTuber SmarterEveryDay has done just that with a video showing what happens when he shoots a bullet at the bulb end of a Prince Rupert’s drop. You can watch the results below in all its 150,000-frames-per-second glory. Does it withstand the impact? Is it unbreakable? We promise you, the slow-mo bit is very cool.

Here’s the science (and spoilers) bit.

The bullet doesn’t actually break the bulb, it bounces off and grazes the droplet, which sends a shockwave through the tail. The tail then immediately shatters, sending stress fractures back down to the bulb and exploding the whole thing.


To put it simply, when the molten glass is dropped into cold water, the outside cools and solidifies almost instantly, while the inside remains molten for longer and cools much more slowly.

Since glass expands when it’s hot and contracts when it cools, as the inside part cools, it tries to pull the already solid, cool outer layer in with it. This makes the bulb even more solid and eventually bullet-proof, holding it all together in a state of tensile stress. That’s a lot of pent up energy.

However, if the fragile, thin, breakable tail end of the drop experiences stress, it will break immediately and send fractures back into the bulb at high speed, releasing all that pent up energy, which causes the bulb to shatter.

Alternatively, you can just watch SmarterEveryDay’s previous video that explains in great detail the wonders of the enigma that is the Prince Rupert’s drop.



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