The Moment A Bullet Turns Into A Flashlight, Caught On Film

July 22, 2023 by Donald Papp 14 Comments

[The Slo Mo Guys] caught something fascinating while filming some firearms at 82,000 frames per second: a visible emission of light immediately preceding a bullet impact. The moment it occurs is pictured above, but if you’d like to jump directly to the point in the video where this occurs, it all starts at [8:18].

The ability to capture ultra-slow motion allows us to see things that would otherwise happen far too quickly to perceive, and there are quite a few visual spectacles in the whole video. We’ll talk a bit about what is involved, and what could be happening.

Spotting something unusual on video replay is what exteme slo-mo filming is all about.

First of all, the clear blocks being shot are ballistic gel. These dense blocks are tough, elastic, and a common sight in firearms testing because they reliably and consistently measure things like bullet deformation, fragmentation, and impact. It’s possible to make homemade ballistic gel with sufficient quantities of gelatin and water, but the clear ones like you see here are oil-based, visually clear, and more stable (they do not shrink due to evaporation).

We’ve seen the diesel effect occur in ballistic gelatin, which is most likely the result of the bullet impact vaporizing small amounts of the (oil-based) gel when the channel forms, and that vaporized material ignites due to a sudden increase in pressure as it contracts.

In the video linked above (and embedded below), there is probably a bit more in the mix. The rifles being tested are large-bore rifles, firing big cartridges with a large amount of gunpowder igniting behind each bullet. The burning powder causes a rapid expansion of hot, pressurized gasses that push the bullet down the barrel at tremendous speed. As the bullet exits, so does a jet of hot gasses. Sometimes, the last bits of burning powder are visible as a brief muzzle flash that accompanies the bullet leaving the barrel.

A large projectile traveling at supersonic velocities results in a large channel and expansion when it hits ballistic gel, but when fired at close range there are hot gasses from the muzzle and any remaining burning gunpowder in the mix, as well. All of which help generate the kind of visual spectacles we see here.

We suspect that the single frame of a flashlight-like emission of light as the flat-nosed bullet strikes the face of the gel is also the result of the diesel effect, but it’s an absolutely remarkable visual and a fascinating thing to capture on film. You can watch the whole thing just below the page break.

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That Ultra-White Paint That Helps Cool Surfaces? Make Your Own!

July 22, 2023 by Donald Papp 49 Comments

It started with [KB9ENS] looking into paints or coatings for passive or radiative cooling, and in the process he decided to DIY his own. Not only is it perfectly accessible to a home experimenter, his initial results look like they have some promise, as well.

[KB9ENS] read about a type of ultra-white paint formulation that not only reflects heat, but is able to radiate it into space, cooling the painted surface to below ambient temperature. This is intriguing because while commercial paints can insulate and reflect heat, they cannot make a surface cooler than its surroundings.

Anecdotally speaking, this painted battery section of a solar recharger gets too hot to touch in full sunlight. But when painted over, it was merely warm.

What really got [KB9ENS] thinking was that at its core, the passively-cooling paint in the research is essentially a whole lot of different particle sizes of barium sulfate (BaSO₄) mixed into an acrylic binder. These two ingredients are remarkably accessible. A half-pound of BaSO₄ from a pottery supply shop was only a few dollars, and a plain acrylic base is easily obtained from almost any paint or art supplier.

[KB9ENS] decided to mix up a crude batch of BaSO₄ paint, apply it to some things, and see how well it compared to other paints and coatings. He wetted the BaSO₄ with some isopropyl alcohol to help it mix into the base, and made a few different concentrations. A 60% concentration by volume seemed to give the best overall results.

There’s no indication of whether any lower-than-ambient cooling is happening, but according to a non-contact thermometer even this homemade mixture does a better job of keeping sunlight from heating things up compared to similarly-applied commercial paints (although it fared only slightly better than titanium dioxide-based white paint in the initial test.)

[KB9ENS] also painted the battery section of a solar recharger with his homemade paint and noted that while under normal circumstances — that is to say, in full sunlight — that section becomes too hot to touch, with the paint coating it was merely warm.

Actual passive cooling can do more than just keep something less warm than it would be otherwise. We’ve seen it recently used to passively and continuously generate power thanks to its ability to create a constant temperature differential, day and night.

Lighting Up With Chemistry, 1823-Style

July 19, 2023 by Dan Maloney 9 Comments

With our mass-produced butane lighters and matches made in the billions, fire is never more than a flick of the finger away these days. But starting a fire 200 years ago? That’s a different story.

One method we’d never heard of was Döbereiner’s lamp, an 1823 invention by German chemist Johann Wolfgang Döbereiner. At first glance, the device seems a little sketchy, what with a tank of sulfuric acid and a piece of zinc to create a stream of hydrogen gas ignited by a platinum catalyst. But as [Marb’s Lab] shows with the recreation in the video below, while it’s not exactly as pocket-friendly as a Zippo, the device actually has some inherent safety features.

[Marb]’s version is built mainly from laboratory glassware, with a beaker of dilute sulfuric acid — “Add acid to water, like you ought-er!” — bathing a chunk of zinc on a fixed support. An inverted glass funnel acts as a gas collector, which feeds the hydrogen gas to a nozzle through a pinch valve. The hydrogen gas never mixes with oxygen — that would be bad — and the production of gas stops once the gas displaces the sulfuric acid below the level of the zinc pellet. It’s a clever self-limiting feature that probably contributed to the commercial success of the invention back in the day.

To produce a flame, Döbereiner originally used a platinum sponge, which catalyzed the reaction between hydrogen and oxygen in the air; the heat produced by the reaction was enough to ignite the mixture and produce an open flame. [Marb] couldn’t come up with enough of the precious metal, so instead harvested the catalyst from a lighter fluid-fueled hand warmer. The catalyst wasn’t quite enough to generate an open flame, but it glowed pretty brightly, and would be more than enough to start a fire.

Hats off to [Marb] for the great lesson is chemical ingenuity and history. We’ve seen similar old-school catalytic lighters before, too.

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Conductive Gel Has Potential

July 18, 2023 by Bryan Cockfield 24 Comments

There are some technologies first imagined in the Star Trek universe have already come to exist in the modern day. Communicators, tablet computers, and computer voice recognition are nearly as good as seen in the future, and other things like replicators and universal translators are well on their way. Star Trek: Voyager introduced a somewhat ignored piece of futuristic technology, the bio-neural gel pack. Supposedly, the use of an organic gel improved the computer processing power on the starship. This wasn’t explored too much on the series, but [Tom] is nonetheless taking the first steps to recreating this futuristic technology by building circuitry using conductive gel.

[Tom]’s circuitry relies on the fact that salts in a solution can conduct electricity, so in theory filling a pipe or tube with a saline solution should function similarly to a wire. He’s also using xanthan gum to increase viscosity. While the gel mixture doesn’t have quite the conductivity of copper, with a slight increase in the supplied voltage to the circuit it’s easily able to be used to light LEDs. Unlike copper, however, these conductive gel-filled tubes have some unique properties. For example, filling a portion of the tube with conductive gel and the rest with non-conductive mineral oil and pushing and pulling the mixture through the tube allows the gel to move around and engage various parts of a circuit in a way that a simple copper wire wouldn’t be able to do.

In this build specifically, [Tom] is using a long tube with a number of leads inserted into it, each of which correspond to a number on a nixie tube. By moving the conductive gel, surrounded by mineral oil, back and forth through the tube at precise intervals each of the numbers on the nixie tube can be selected for. It’s not yet quite as good as the computer imagined in Voyager but it’s an interesting concept nonetheless, not unlike this working replica of a communicator badge.

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High School Student Builds Inexpensive Centrifuge

July 11, 2023 by Bryan Cockfield 31 Comments

Having a chemistry lab fully stocked with all necessary equipment is the dream of students, teachers, and professors alike, but a lot of that equipment can be prohibitively expensive. Even in universities, labs are often left using old or worn-out equipment due to cost. So one could imagine that in high schools this is even a more pronounced problem. High school student [Aidan Miller] has solved this problem with at least one piece of lab equipment, bringing the cost for a centrifuge down to around $10 USD.

Part of the savings is due to the fact that [Aidan] has put together a smaller sized centrifuge, known as a micro-centrifuge. The function is still the same though, spinning samples to separate them out the constituents by weight. The 3D printed base of the centrifuge houses a switch and 9 V battery and also holds a small motor which spins the rotor. The rotor itself is also 3D printed, and needed to be a very specific shape to ensure that it could hold the samples properly at high RPM and maintain reasonable balance while spinning.

As a project it’s fairly simple and straightforward to build, but the more impressive thing here is how much it brings down the cost of lab equipment especially for high school labs that might otherwise struggle for funding. Of course it requires the use of a 3D printer but the costs of those have been coming down significantly as well, especially for things like this portable 3D printer which was also built by a high school student.

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Stirring Up 3D-Printed Lab Equipment

July 9, 2023 by Bryan Cockfield 18 Comments

Magnetic stirrers are a core part of many chemistry labs. They offer many advantages for ensuring the effective mixing of solutions compared to other methods of stirring, including consistency, precise control, operation within closed systems, and of course, hands-free automatic operation. With so many reasons for employing a magnetic stirrer, it’s not too surprising that [Joey] would want one. He built his using 3D-printed parts rather than purchasing it.

The magnetic stirrer uses a 3D-printed enclosure for the base. Inside is a PWM controller which sends power to a small DC motor. A 3D-printed arm is attached to the motor, which hosts a pair of magnets. As the arm spins inside the enclosure, the magnetic fields from the magnet couple with the stir bar inside the mixture, allowing it to spin without any mechanical link to the stirring device and without any input from the user. [Joey] has also made all the 3D-printed parts for this build available on Printables.

While magnetic stirrers aren’t the most complicated of devices (or the most expensive), building tools like this anyway often has other advantages, such as using parts already on hand, the ability to add in features and customizations that commercial offerings don’t have, or acting as a teaching aid during construction and use. It’s also a great way to put the 3D printer to work, along with this other piece of 3D-printed lab equipment designed for agitating cell cultures instead.

Cooling Paint You Can Actually Make

July 3, 2023 by Jonathan Bennett 49 Comments

[NightHawkInLight] has been working on radiative sky paint. (Video, embedded below.) That’s a coating that radiates heat in the infrared spectrum at a wavelength that isn’t readily absorbed or reflected by the atmosphere. The result is a passive system that keeps materials a few degrees cooler in direct sunlight than an untreated piece in the shade. That sounds a bit like magic, but apparently the math checks out.

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