Prince Rupert's drop explosion. The mystery of Prince Rupert's mysterious drops has been revealed. Explosive glow of Rupert's drop

The blob looks like a tadpole with a bulbous head and a long, thin tail. The head is so strong that it can withstand a hammer blow, and bullets fired at point-blank range are destroyed upon impact - yes, it’s bullets, not glass. However, if you flick the tail of the drop with your finger, it will turn the entire drop, including the tough glass head, into powder.

Prince Rupert's Drops (also known as "Batavian Tears" and "Bolognese Flasks") are formed by dropping liquid glass into cold water, causing the outer surface of the drop to immediately solidify while the glass inside remains molten. The cooled outer layer tries to contract while the molten inner layer tries to expand. During the crystallization process, opposing forces acting on the droplet head make it unusually strong and fragile at the same time. It is like a stone arch - the structure is under extreme tension, which is precisely what prevents it from falling apart. But if you remove the cornerstone, the arch will collapse.

Prince Rupert's Drops were first discovered in Germany in the 1640s. They were originally created by glassmakers in Mecklenburg (Northern Germany) and were sold as toys and curiosities throughout Europe, where they were called variously, such as "Prussian tears" or "Dutch tears". Glassmakers carefully guarded their secret, leading to a number of theories as to how the drops were made.

An amateur scientist from England, Duchess Margaret Cavendish, after weeks of experimenting with dozens of samples in her laboratory, came to the conclusion that a small amount of a volatile material was introduced into the head of the drop, which reacted violently when exposed to air.

In 1660, Prince Rupert of the Palatinate, Duke of Cumberland and one of the founders of the Royal Society, brought with him several glass drops to demonstrate them to scientists and King Charles II. As you probably already guessed, they were named after him.

Robert Hooke, who was responsible for carrying out the experiments to members of the public, made an important breakthrough by suggesting that it was the cooling of glass after immersion in water that caused the strange properties of the drops, although a fuller understanding of the mechanics did not become available until three centuries later.

It wasn't until 1994 that scientists from Purdue University and the University of Cambridge, using high-speed imaging to observe droplet breakup, concluded that the surface of each droplet was under high compressive loads, while the interior was under the influence of high-tension forces - in a state of uneven balance, which can easily be disrupted by breaking the tail. Experiments show that the bulbous head can withstand compression forces of up to 7000 kilograms per square centimeter. It was also estimated that destructive cracks were spreading along the tail and head at an astonishing speed of 6,500 kilometers per hour.

Subsequently, working with the Tallinn University of Technology in Estonia, the researchers discovered that in order to break a droplet, it is necessary to create a crack that can penetrate its internal stress zone. The outer compression layer is very thin: it is only about 10 percent of the diameter of the droplet head, but it is incredibly strong. Since surface cracks typically grow parallel to the surface, they cannot enter the stress zone. But if the tail cracks, the cracks will enter the stress zone and release all the stored energy, causing the drop to collapse.

Tempered glass, which is typically used in cars and mobile phones, is made using the same principle. It is quickly cooled into its molten form by cold air, creating internal tension that allows the surface to remain compressed at all times. The compression prevents the cracks from growing, but when the glass finally breaks, it shatters into thousands of small pieces. This is why car windshields shatter into small pieces upon impact, but they are coated with a special layer of adhesive that prevents particles from entering the vehicle interior and causing injury to passengers.

“Tensile stress is what typically causes materials to fail in a manner similar to tearing a sheet of paper in half,” says Koushik Viswanathan of Purdue University. “But if you change tensile stress to compressive stress, then you make it harder for cracks to grow, and that’s exactly what’s happening at the head of the Prince Rupert Drop.”

Batavian tears or Bolognese flasks, as well as Prince Rupert's drops, are frozen drops of tempered glass that have extremely durable properties. They were brought to England by Prince Rupert of the Palatinate in the mid-17th century. Then they attracted the close attention of scientists.

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Most likely, such glass drops have been known to glassblowers since time immemorial, but they attracted the attention of scientists quite late: somewhere in the middle of the 17th century. They appeared in Europe (according to various sources, in Holland, Denmark or Germany). The technology for making “tears” was kept secret, but in reality it turned out to be very simple.

If you drop molten glass into cold water, you get a tadpole-shaped drop with a long, curved tail. At the same time, the drop has exceptional strength: you can hit its “head” with a hammer and it will not break. But if you break the tail, the drop instantly scatters into small fragments.

The frames recorded using high-speed photography show that the front of the “explosion” is moving along the droplet at high speed: 1.2 km/s, which is almost 4 times the speed of sound.

As a result of sudden cooling, the glass drop experiences strong internal stresses, which causes such strange properties. The outer layer of the drop cools so quickly that the glass structure does not have time to rearrange itself. The core is stretched, and the outer layer is compressed. Tempered glass is obtained in a similar way - however, it does not have that tail, which can so easily break the shell.

Let me introduce you to one of the interesting properties of glass, which is commonly called Prince Rupert's drops (or tears). If you drop molten glass into cold water, it will harden in the shape of a drop with a long thin tail. Due to instant cooling, the drop acquires increased hardness, that is, it is not so easy to crush it. But if you break off the thin tail of such a glass drop, it will immediately explode, scattering the finest glass dust around itself.

Today, the mechanism of “work” of Dutch tears has been thoroughly studied. If molten glass falls into cold water, it quickly solidifies, accumulating incredible mechanical stress. Let us conditionally distinguish the outer layer and the inner core in the drop. The droplet cools from the surface, and its outer layer contracts and decreases in volume while the core remains liquid and hot.

After the temperature inside the ball drops, the core will begin to shrink. However, the already hard outer layer will resist the process. With the help of intermolecular forces of attraction, it tenaciously holds the nucleus, which, when cooled, is forced to occupy a larger volume than if it cooled freely.

As a result, forces will arise at the boundary between the outer layer and the core, pulling the outer layer inward, creating compressive stresses in it, and the inner core outward, creating tensile stresses in it. These stresses when cooling too quickly are quite significant. So the inside of the ball can break away from the outside, and then a bubble forms in the droplet.

If the integrity of the surface layer of the tear is disrupted, the tension force is immediately released. The frozen glass drop itself is very strong. It can easily withstand a hammer blow. However, if you break its tail, it collapses so quickly that it is more like a glass explosion.

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We have never been able to find the original source of this widespread belief: not a single sheet of paper can be folded twice more than seven (according to some sources, eight) times. Meanwhile, the current folding record is 12 times. And what’s more surprising is that it belongs to the girl who mathematically substantiated this “riddle of a sheet of paper.”

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You may have experienced strange physical sensations in high-speed elevators: when the elevator starts going up (or slows down when moving down), you are pressed to the floor, and it seems to you that you are momentarily heavier; and at the moment of braking when moving up (or starting when moving down), the floor of the elevator literally disappears from under your feet. You yourself, perhaps without realizing it, are experiencing the effect of the principle of equivalence of inertial and gravitational masses. When the elevator starts upward, it moves with an acceleration that is added to the acceleration due to gravity in the non-inertial (accelerating) frame associated with the elevator, and your weight increases. However, as soon as the elevator reaches “cruising speed”, it begins to move evenly, the “gain” in weight disappears, and your weight returns to your usual value. Thus, acceleration produces the same effect as gravity.

The movement of a physical body in one dimension does not depend on its movement in the other two dimensions. For example, the flight path of a cannonball is a combination of two independent trajectories of motion: uniform horizontal motion with the speed imparted to the cannonball, and uniformly accelerated vertical motion under the influence of gravity.

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The English nobility of the 17th century were reputed to be inquisitive and did not shy away from science. King Charles II even died from his passion for alchemy: already in our time, mercury was discovered in his hair in a concentration incompatible with life. Charles II's cousin, Prince Rupert, was famous for his passion for scientific wonders, both theoretical and practical.

It was this Prince Rupert, also known as Duke Ruprecht von der Pfalz, who brought drop-shaped glass castings with long curved tails to London. Presenting them as a gift to the king, Rupert said that this was a recent German invention, and that the strength of glass drops exceeded the strength of steel.

Rupert hid the production method from the king, citing ignorance. Although now we understand: the prince was silent solely for the sake of greater mystery...

Charles II gave the resulting drops for analysis to the Royal Scientific Society. From that moment on, the glory of Rupert's drops began.

Properties of Rupert's Drop

The strength of Rupert's glass drops was, however, uneven. While the head of the drop could withstand any blow, the tail - especially the tip of the tail - was highly vulnerable. The strangest thing is that the destruction of the tail led to the instant disintegration of the entire glass casting! Moreover, it will decay explosively, with the instantaneous scattering of the smallest fragments!

Members of the Royal Scientific Society sent letters asking about the nature of the unusual glass to all available areas. The popularity of the unusual toy among the London nobility began to grow. Prince Rupert made a good business, either selling amazing glass drops at a high price, or strengthening ties with interesting gifts.

Soon the situation began to become clearer...

Rupert's Drops come from...?

According to information received from the Dutch, the Danes began to play with Rupert's drops before the Germans - but the secret of making durable glass castings came to Denmark from Italy. The entire south of Europe knows them as “Bolognese flasks” and sees nothing complicated in making glass drops.

Rupert's Drops are easy!

After conducting a series of experiments, scientists of the Royal Society of London determined: to obtain the most successful Rupert's drops, glass should be taken as pure as possible, and heated no higher than to the degree of complete softening - otherwise a drop falling into the water will become covered with cracks.

We were satisfied with that...

A modern take on Rupert's drops

Rapid cooling of a glass drop in an environment that effectively lowers the temperature leads to compaction of the outer layers of the body, compression of the mass with simultaneous stretching of the still hot core of the casting.

The strength of Rupert's drop is not at all infinite, and is only four times stronger than glass produced using conventional technologies. However, strength indicators strongly depend on the composition of the glass charge, and dense quartz glass in tempered and droplet form is really capable of withstanding the blows of a forging hammer.

But only if you don’t hit Rupert’s drops on the thin, fragile tail!

Break Rupert's Drop

That is why, by the way, in ancient Europe, Rupert's drop of content quickly migrated from the category of amusing curiosities to the category of dangerous entertainment.

Modern experimenters do not stop experiments with Rupert's drops. Particularly spectacular are attempts to destroy glass droplets with a rifle shot. A soft lead bullet hits the head of Rupert's drop with a force significantly greater than the force of a blacksmith's hammer, but the bullet is unable to break the tempered glass.

The shock wave arising in the glass mass turns out to be destructive for the thin tail of Rupert's drop. When the vibration pulse passes through thin glass, rapidly expanding cracks appear. At a speed of more than 1 km/s, the cracks grow throughout the droplet body, multiply, expand and actually explode the glass.

Explosive glow of Rupert's drop

The bluish-red flashes of triboluminescence of the disintegrating Rupert drop are the glow of atoms of atmospheric gases excited by weak electrical discharges. Electricity is generated by molecules

Prince Rupert's Blob looks like a glass tadpole created by a novice glassblower, but it's so strong it can't even be broken with a hammer. However, it is enough to lightly hit it on the “tail” and it crumbles into powder. Scientists have been trying to find the reason for these inexplicable qualities for almost 400 years, and now a team of researchers from the University of Cambridge and Tallinn University of Technology in Estonia finally have the answer.

Batavian tears or Prince Rupert's drops first appeared in the 17th century and became famous when Prince Rupert of Bavaria presented five of these trinkets to King Charles II of England. They were submitted to the Royal Society for study in 1661, but despite almost four centuries of research, an explanation for their strange qualities has only now been found. The drops are made from molten glass with a high coefficient of thermal expansion and dropped into a vessel of cold water. The molten glass instantly freezes into a characteristic droplet shape.

To study Prince Rupert's drops, scientists used a technique where a transparent 3D object is placed in an immersion bath to allow polarized light to pass through it. Changes in the polarization of light within an object correspond to voltage lines. Previous work by Tallinn and Cambridge physicists, dating back to 1994, included filming a droplet exploding at almost a million frames per second. In the video you can see how, after the “tail” is damaged, the cracks spread drop by drop at a speed of about 6,500 kilometers per hour.

The new study found that the compressive stress of the glass at the "head" of the drop is about 50 tons per square inch, making it as strong as steel. This happens because the outside of the drop cools faster than the inside. Thus, enormous pressure is injected into the center of the “head” of the drop, which is compensated by stretching.

As long as these forces remain in balance, the droplet is very strong and can withstand significant loads. But if the “tail” is damaged, this balance is disrupted, and many small cracks spread parallel to its axis. This happens at such a high speed that it resembles an explosion.