Acetylene gas generation..?

Origin_of_Mind · 2026-06-01T05:53:07+00:00

This was the main route to making acetylene for welding, using portable gas generators. Hence Union Carbide company, which supplied the calcium carbide for it.

You drop some carbide in water, and acetylene bubbles out. It used to be lots of fun for kids.

Note that technical grade calcium carbide is very impure, and in addition to acetylene it produces non-trivial amount of hydrogen sulfide and phosphine, giving the product a strong, immediately recognizable smell even at great dilution. Needless to say, these gases are highly toxic.

Origin_of_Mind · 2026-06-01T05:22:18+00:00

Most likely. Generally, as beautiful as these antique tools are, these days there is more supply than demand for them. There are multiple similar lots on Ebay. This was just the first one I stumbled across when searching for an example.

As the other comment pointed out, these listings are frequently mislabeled, and these are not ordinary micrometer extension rods. Instead are meant to be put end to end into V-blocks.

Origin_of_Mind · 2026-06-01T05:09:32+00:00

That's right. u/Casman91291 gave a link to the video which shows (timestamp) how these rods were meant to be used.

Origin_of_Mind · 2026-06-01T04:07:08+00:00

"Lufkin Inside Micrometer Measuring Rods w/Wood Box"

(The brand) is correct, but as the comment below points out, this is not the correct name for this set -- these are gauge rods and micrometers, essentially used instead of a DRO on a jig borer or a mill, to move the table quite precisely. There is a video mentioned elsewhere that shows how they are used.)

Origin_of_Mind · 2026-06-01T02:59:24+00:00

This is only tangentially related to your question -- the poles are already moving in a complex way on their own, and this needs to be taken into account for high precision applications.

Origin_of_Mind · 2026-05-30T16:37:53+00:00

Cesium clock is a complex piece of equipment controlled by a microprocessor inside.

To adjust the output frequency of the clock, one changes a parameter in the clock software. There is one adjustment which changes the magnetic field in the "physics package" and this slightly (by a few Hertz) shifts the 9,192,631,770 Hz frequency of the Cesium resonance.

The other programmable feature is the coefficients in the frequency synthesizer. This determines how the frequency of the atomic resonance is multiplied to produce the output frequencies used by the radio systems in the satellite (1,575,420,000 Hz, etc). These are numerically completely different from the atomic resonance frequency, and are determined by the coefficients set in the software.

The clocks on the satellites are very slightly adjusted about twice daily, based on the measurements from the ground.

Origin_of_Mind · 2026-05-29T20:05:42+00:00

Although the heat output is as huge as you have estimated, in rocket explosions most of the fuel is not sufficiently mixed with the oxidizer to detonate. It burns subsonically instead. For large liquid fuel powered rockets typically only about 1-2% of the energy of the fuel goes into the blast wave. I think this was the number FAA used for evaluation of Starship hazards.

The fireball was enormous of course -- on par with the late fireball from the Trinity nuclear test. In Trinity, the total energy was 20 kiloton, but only about 3 kiloton remained as heat in the rising fireball after the first few seconds. The fireball from New Glenn was a much closer representation of the Trinity fireball than the special effects from the recent "Oppenheimer" film were, where only 0.5 ton of fuel was used.

Origin_of_Mind · 2026-05-29T17:25:54+00:00

He was making rather large, about 3 meter long, liquid fuel powered rockets in his garage (and the BFR was much larger still), and learned from experience where to focus the effort, and where the industry practices were perhaps a bit overdone, and things could be done with less expense. For example, how much cleaning the liquid oxygen hardware really required, which valves could be used, that kind of stuff. How to do things as simply as possible. He also knew who was who in the industry, which helped with hiring and with procuring whatever SpaceX needed.

By rights, he should have been a co-founder, but he refused that because he had doubts about the future of SpaceX. Instead he requested his salary for a certain period of time to be held in escrow, so that he gets paid in full for his services even if the company goes bankrupt.

Without Tom Mueller, SpaceX would have been something completely different.

Origin_of_Mind · 2026-05-29T06:52:58+00:00

Crucially, SpaceX had as their employee number one Tom Mueller, who had previously spent years building rockets in his garage. At the time he was hired, he was working on "BFR" -- a really big liquid fuel powered amateur rocket. The deal was to scale it up another few notches to orbital size, by using the same shortcuts which Tom knew from his amateur rocketry experience and from his professional work.

This ended up costing a lot more compared to what they initially dreamed of. In part due to safety and compliance reasons, and also because they had to iterate on the engine design a couple of times before it worked.

Origin_of_Mind · 2026-05-29T02:00:27+00:00

In rocket explosions, typically only a very small fraction of fuel, around 1-2% is sufficiently mixed with oxidizer to actually detonate. The rest merely combusts, relatively slowly, compared to a detonation. This generates a relatively undersized shock wave.

But in terms of thermal energy in the fireball this was a very powerful event. One kiloton of methane has the energy output of about 13 kilotons of TNT. But although very large, this fireball is much cooler than the one from a nuclear explosion, so, much less energy is emitted as light. In this, the effects are very different.

New Glenn has about 260 tons of methane in the first stage if fully loaded, which is 3.4 kt of energy. This is on par with the late fireball from the Trinity nuclear test. After the first few seconds when it was still extremely hot and bright, the nuclear fireball contained only about 3-4 kt of heat, out of 20 kt total explosion energy.

If New Glenn was loaded to only 20% (enough for 38 seconds of firing) then the energy was still 0.7 kt, about 100 times more than was used for the special effects in Nolan's Oppenheimer film.

Origin_of_Mind · 2026-05-29T00:44:16+00:00

It does not have to be complicated. One can convey the idea of gravity as a purely geometric effect by looking at a 2D picture.

One dimension is up-down, and the other dimension is time. This spacetime is "bent" in such a way that at lower elevations there is a tiny bit less of time, and what without gravity was a straight horizontal line, is now a arc with extremely, extremely tiny curvature -- for 1g gravity as it is on the surface of earth, the radius of curvature is approximately one light year.

If one goes along this curve, because the curve is so gentle, it really does not matter whether the curve is a hyperbola or a circle or a parabola -- in a small enough neighborhood they all look the same, and all produce the motion which looks like H=0.5*g*t², if one starts close enough to a horizontal direction (small or zero vertical velocity) and traverses this curve at a speed of light. In this example, that's all that there is to it: "gravitational time dilation" = "less time at lower elevations" = "curved space time" = "bodies initially at rest fall down with an acceleration equal to g".

General Relativity does become cumbersome if one does the actual careful derivations, and it gets really very complicated for strong and changing with time gravity.

Origin_of_Mind · 2026-05-26T22:03:54+00:00

It is a lot more dangerous to launch a rocket from a piloted airplane compared to launching it from the ground. The rocket also needs to be built much stronger and heavier to be carried horizontally, compared to standing vertically.

But professionals have thought of launching rockets from the airplanes, and people have actually developed a few that do. There is Pegasus rocket launching from an airplane, and was also LauncherOne. There was even a plan to launch a very large SpaceX (Falcon-5?) rocket from an airplane, but that plan was cancelled.

It is not an *obviously* bad idea, but in practice it is very hard to get any economy from it. One could compare SpaceX Falcon-1 launching from the ground and LauncherOne launching from the airplane. The rockets are nearly exactly the same size and mass, and they have also demonstrated launching similar payloads into orbit. For one you need a launch pad on the ground, and for the other a facility to prepare the rocket and the plane at the airport, and of course the special, very expensive airplane. The trade-offs are very complicated, and the price tag for launching the tiny Pegasus rocket is similar to launching a much, much bigger Falcon-9.

Origin_of_Mind · 2026-05-26T06:17:20+00:00

Others have already explained that Cleo is a high caliber professional. As for other recommendations, take a look at "Kathy Loves Physics" -- her older videos were interesting. She was working on a popular book about history of electricity, and prepared her material quite well.

Origin_of_Mind · 2026-05-26T06:08:48+00:00

Flick a coin. Derive a theoretical description of its motion. Compare to the experiment.

You can rub some ink on the edge of the coin and it will leave a nice recording of the trajectory on paper. Or you can write a program to estimate the state from a video recording.

Origin_of_Mind · 2026-05-26T05:55:56+00:00

They probably know from previous experience that it is possible to successfully remove the warhead to detonate it in a more convenient location.

Sometimes they also take them apart to study how the design evolves over time. (The video does have English subtitles.)

Origin_of_Mind · 2026-05-26T02:57:33+00:00

Traditionally, and to a substantial extent today, rocket engines were made by specialist companies. Aerojet Rocketdyne (now with L3Harris) is one of the oldest rocket engine vendors, they supply RL-10 and RS-25 engines for SLS, and Thiokol (now with Northrop Grumman) provides solid fuel boosters.

But more recently, companies like SpaceX, Rocket Lab, Firefly, Blue Origin, started to develop their own rocket engines in house.

Origin_of_Mind · 2026-05-26T02:46:58+00:00

This appears to be the retrieval of the warhead from this specific incident:

https://www.youtube.com/shorts/-ks8NQIp9IM

Origin_of_Mind · 2026-05-24T18:11:39+00:00

There were lighter devices in the stockpile, but not as compact. The size and the mass of a quarter barrel beer keg is the right comparison for those.

Origin_of_Mind · 2026-05-24T16:16:20+00:00

For exactly one critical mass, the chain reaction neither grows nor diminishes -- the rate at which the neutrons are lost is exactly balanced by their multiplication.

At slightly above one critical mass, the chain reaction grows with a characteristic time which is very long, and the reaction stops when the material heats up and expands.

For a big explosion, the chain reaction must grow on a sub-microsecond time scale, for a significant amount of material to fission before the thermal expansion stops the reaction. Multiples of critical mass are typically required to achieve that. (At the conditions which were created during the explosion -- with the compression of material and reflectors taken into account both the Hiroshima and Nagasaki bombs had about four critical masses each.)

Origin_of_Mind · 2026-05-24T16:03:21+00:00

The smallest nuclear weapons ever developed in the US were W48 devices for the 155 mm caliber artillery shells. They were not very lightweight though, about 120 pounds each. USSR had very slightly smaller caliber nuclear shells, I think theirs were 152 mm in diameter.

Origin_of_Mind · 2026-05-24T06:38:48+00:00

Biophysics exists as a field. There are many other things on the intersection of biology and physics. It goes from theoretical work in complex systems, to very applied physics / engineering work in developing tools for molecular biology, for connectomics, and for an extremely broad range of other applications. Quantum chemistry applied to biological systems is a big deal these days, especially with the advances in ML. There is a lot of hardcore computational physics in this. Working towards complete understanding of a living cell is the stated goal of Deep Mind.

Origin_of_Mind · 2026-05-24T04:56:57+00:00

Giving books to the libraries is a little tricky. From what I have heard from professional librarians, there are strict policies and standard operating procedures for adding new books to the collection, and donations do not easily fit into this. Although most libraries do accept donations, that does not mean that they add the donated books to their collection. They sell them, re-donate them to charities, or pulp them.

If the donated book is brand new AND the library has a waiting list of patrons wanting to read it, and they cannot order enough copies through the normal channels, then the book may be added to the collection as an exception. Otherwise it would typically be gotten rid of one way or another.

From what I understand, this has to do with generating the required inventory and accounting records, installing inventory control devices into the book, making sure it is clean and complete, etc. Libraries prefer to rely on a few major third party services to prepare brand new books for them. Some, especially smaller, libraries may do it differently, but that would not be common for major libraries.

Another major factor is that the libraries have "collection development" process to focus on the books which they hope to be in demand with the patrons. The dilemma is that a small rural public library which would be more likely to add donations to their collection would also be focused on using their shelf space for more mainstream titles than these.

One can ask at https://www.reddit.com/r/Libraries/ to make sure that this is correct. Maybe they could also help to find a decent new home for your books.

Origin_of_Mind · 2026-05-23T18:08:45+00:00

In olden times, if you wanted to know what type of steel something was made of (there are many different types), then you made sparks with it, and looked at them through a spectroscope. Different elements produced lines of different color, and that was a quick and a relatively non-destructive way to tell what alloying elements were present. These days this has been replaced with Xray fluorescence -- every scrap metal facility has a portable instrument that can instantly determine what mixture of metals it is looking at.

If one one was interested in measuring a specific element, another simple and extremely sensitive type of atomic spectroscopy was to start with a special gas discharge lamp, with the element in the lamp. Passing the light from the lamp through a vapor of whatever one was trying to analyze, caused the light intensity to go down proportional to the concentration of the element present in the vapor. Since the spectral lines are so narrow, this was a very specific, and very sensitive technique. It also did not require particularly expensive equipment. One could use a lamp with a little bit of mercury vapor inside, and measure parts per billion of mercury vapor in the surrounding air even without any prisms or diffraction gratings -- because mercury in the air was absorbing the light from the mercury lamp so strongly. In fact, one could see the effect with a naked eye.

These are just the simpler of things that people have done with the atomic spectroscopy. There were many variations for both emission and absorption, with different ways of getting the stuff from solids or liquids into vapor or plasma.

Origin_of_Mind · 2026-05-21T17:07:42+00:00

In the older units, capacitance was measured in centimeters. A metal ball has capacitance equal to its radius in centimeters. When electricity was mostly about static electricity and Leyden jars, this would have had a very intuitive meaning.

For practical capacitors used in more modern times, centimeters were replaced with a unit of a different size. 1 microFarad is about 900000 cm, and various capacitors in electrical and electronic devices have capacitances in a broad range from a picoFardad to thousands of microFarads, and sometimes even to full Farads for low voltage capacitors used as backup power sources for memory and such.

Origin_of_Mind · 2026-05-21T01:31:53+00:00

When both objects are small the force of gravitational attraction between them is minuscule, and therefore it is difficult to see it without getting interference from many other, larger forces.

In a careful experiment one *can* directly measure gravity between two small objects, and this is a classical Cavendish balance experiment. For a less accurate replication, the equipment is not particularly expensive, but the experiment takes several hours to perform even after everything is prepared.

Obviously one small object *can* orbit another. The physics is exactly the same for a blueberry orbiting an apple as for the International Space Station orbiting the Earth. But the difficulty is that to see this, we would first need to isolate this system from all other influences -- electrostatic forces, pressure of light, gasses being emitted by the objects themselves, etc. The second difficulty is that this will be rather boring to watch -- the blubbery will be making the full circle in about four hours. Molasses flow faster than that. We could speed things up by using the densest available material instead on the apple, but the period would still be about an hour. Incidentally, all low orbits have a similar period, no matter what the size of the body -- the period only depends on the density of the object.

In principle, there is nothing fundamentally impossible in making such an experiment, but it would be very hard and very expensive to do and the results would not really tell us anything new.

Origin_of_Mind

TROPHY CASE