Make Prince Rupert's Drops - Glass Turned Hand Grenade





Introduction: Make Prince Rupert's Drops - Glass Turned Hand Grenade

Prince Rupert's Drops are one of the most spectacular physics demonstrations I have witnessed. They are formed by a drop of molten glass being cooled rapidly in water in such a way that stress in the core is at a tipping point that requires only a slight imbalance to explode. Even so, the stresses are organized pressing against each other so that if the drops of glass are impacted from the side they can withstand direct hammer blows. It is not until the tail of the drop is fractured that the forces within the glass lose their balance and release in an explosion, fracturing through the glass at a rate three times faster than a .50 BMG sniper rifle bullet.

At 3600 meters per second, the rate that Prince Rupert's Drops fracture surpasses the rate of any other release of kinetic energy that I am aware of. Reactions involving chemical and nuclear energy are typically the only events that are capable of accelerating to this this extreme speed.

The drops are quite simple to make as the above video demonstrates, so long as great care is placed into safety regarding eye protection and care to avoid burns. The glass from these drops can be thrown great distances, so they should be broken within confinement to avoid throwing shards all over the work area.



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Can you make Prince Rupert's Drops out of SLS glass, such as that used in beer bottles?


Showing the stresses with the filter and your monitor was pretty rad.

When I studied engineering back in the '70s, we learned about using polarizers to show up stresses. We used a light source behind a fixed polarizer. The piece under investigation was placed between the fixed polarizer and a moveable polarizer. You would change the front polarizer to get the best color fringes. One project was to understand the function of the flying buttress in the mideival cathedrals. A model of the cathedral was made with acrylic sheets with weights based on calculated loads. The structure was heated to annealing temperatures and then slowly cooled. This locked in the stresses so the pieces could be dismantled and individually inspected in the polarizers to see where the stresses concentrated.
If you have a LCD screen on your computer, this is basically a backlight going through one polarizer, the liquid crystal layer (whose orientation changes the polarization with applied voltage) and another polarizer. The emitted light from a white screen is polarized so putting a stressed transparent substance between the screen and an external polarizer will show stress fringes.

Hey that was a great information burst, thanks for taking the time out to share. Im gonna bake me in some stress!

I have been practicing making the Prince Ruperts Drop for a few weeks now. The drop part comes out fine, but for the life of me cannot get one to break, or rather explode from clipping the tail. I've sheered that thing down to the bulb of the glass, and yet they're still 100% in tact, ( minus the tail I snapped off like 3 times). I would like to make them as gifts, but is there a reason I cant get them to shatter?



it is the breaking off of the tail that triggers the effect not the heating of the glass. The cooler the better.

it's the fracturing of the tail that causes the reaction. If I can use that term, not the heating of the glass . In fact the cooler the better.

For those wondering, yes, you can make the drops from Boro (Pyrex) however, unlike soft glass or soda glass, they will not explode. Also, it isn't really an explosion. As said in the video, the forces pull the glass inwards. When the tail is snipped, it breaks the high stress layer of the glass, which then allows the glass to crumple inwards at high speeds. Because of all the glass flying inwards on itself, kinetic energy forces the glass to repel outwards after bouncing off itself. It is more of an implosion, than an explosion.

RDX Explosive velocity 8750 m/s
PETN Explosive velocity 8400 m/s
Trinitrotoluene Explosive velocity 6900 m/s
But these are all chemical explosive's

Self disassembly at 3600 meters per second is fantastic.

Not only is it fantastic, but it is still the fastest non chemical explosion/implosion known to man. Although, magnets are still placeholders of the strongest kinetic explosion/implosion speed.

How big can they get? Just wondering if a REALLY big one, mounted between two polarizers, driven by sunlight, might be made to "project" those beautiful moiré patterns, something like the way a properly-oriented prism scatters rainbows....