I don't know the fluid dynamics of mushroom clouds from explosions from formal study, but my best guess judging from how they rise is that it looks like the hottest gases in the middle rise fastest due to buoyancy and the gases on the periphery rolls under to fill the space vacated by the hottest portion of the gas rising, resulting in a mushroom shape. Some of the smoke and cooled gases from the periphery linger in the wake of the rising ball of hot gas, producing the portion of the mushroom cloud that looks like the stem of a mushroom.

If mushroom clouds form from rising hot gases, would a large but cold explosion not produce a mushroom cloud? For example, if a large sealed pressurized tank of liquid nitrogen were to heat up enough where it over-pressurizes and explodes, there could be a huge explosion from the pressure, but all the gases involved in the explosion would be extremely cold. Would such an explosion not produce a mushroom cloud?

If such an explosion were to happen high in the air, would this result in an upside-down mushroom cloud as the ball of cold gases falls through the atmosphere?

I was following a tutorial that required inserting a datum plane in order to make a sketch for a part, but I noticed that the Part Design toolbar in FreeCAD on my computer was missing the Datum Plane button.

Datum Plane button in the Part Design toolbar.

My first question is this: why might it be missing? I don't remember doing anything that might have removed it.

I poked around the interface, and found that I could bring up the toolbar selection window by right clicking the toolbar area, which had an option to customize the toolbars:

https://preview.redd.it/zltnbkff98jh1.png?width=1232&format=png&auto=webp&s=52e9f135d9f32ddce3f1b6f97b61c20241d3f217

I figured I could use this customize feature to put that Datum Plane button back into the Part Design toolbar. I clicked on the Toolbar tab, and found the Datum Plane tool with a quick search:

https://preview.redd.it/0ks5kzdka8jh1.png?width=2260&format=png&auto=webp&s=6d991c3e5ed6819cb8aaf513bd608c61f74f7220

But nothing I clicked in this interface puts this tool onto the toolbar. I tried dragging and dropping, and clicking all of the buttons in this window, but nothing works.

The arrow keys don't do anything.

The New button makes a new toolbar.

I don't want to delete this tool, and I don't want to rename it.

What do I do to get this button back onto the toolbar that it is supposed to appear in?

EDIT: Updated with some distinctions I've learned for what each knife can or can't do. /EDIT

I found a fascinating design enigma. Take a look at these two fish fillet knives. The top one is the Japanese Deba, their traditional fish fillet knife. The bottom is the western style fish fillet knife. Both blades are optimized to do exactly the same task:

Visual comparison of the Japanese deba knife and the western fillet knife.

The deba's blade is short, thick, and broad. It is extremely thick, often 3mm even 4mm at the spine, single-beveled on the right side and hollow-ground on the left, completely stiff and inflexible. The spine of the deba swoops down to meet the edge, which has minimal curvature. The blade heel is pointy, and has a space that's at least a finger's width between it and where it gets inserted into the handle.

The western fillet knife has a long narrow blade (typically a couple of inches longer than the equivalent deba). It is thin, double-beveled, and very flexible. The spine of the blade curves upward, and the blade increasingly curves as it approaches the tip, which narrows down to an acute point. There is no appreciable heel on this knife. It extends down to a bolster or hand guard where the user holds it right up against where the blade emerges from the handle.

These two knives are designed to do the same task: break down and remove the fillet of a fish off of the bones with minimal loss of meat. I've seen videos of each of these knives being used, and the technique doesn't look substantially different. And yet every design decision in each of these blades was intended to optimize its function, which is to fillet fish.

EDIT: Apparently the deba is used in ways that the fillet knife is not able to be used: the deba is often used to kill the fish by whacking it across the head with the thick spine of the blade, chop through the spine of the fish or to split the fish head in half, whereas the fillet knife is too delicate to do that. The fillet knife lets the user fillet the fish in on continuous stroke.

Japan also has another style of blade that is more like the western fillet knife, the honesuki. It has a thinner blade, but the blade is not flexible like the fillet knife./EDIT

It gets even stranger. The Taiwanese fish knife, which is used for the same task looks radically different from both of these. The top row of blades is used for large fish like tuna and salmon. The bottom row has the sizes which are the counterpart to the deba and the fillet knife:

Taiwanese style fish knife.

The blades of these knives are extremely thin, double-beveled, extremely broad, with an extremely curved edge. There is no bolster on these knives; the blade is seated right against the handle.

The crazy thing about this is that this knife was also designed for the same task of breaking down fish quickly and efficiently. And yet in the course of optimizing the design to suit the function it is intended to perform, these knives ended up with radically different, practically opposite designs.

EDIT: The Taiwanese fish knife, particularly the large ones with the extreme belly curve, are intended for breaking down large fish like tuna, sword fish, and sharks. The heft of the blade lets it chop through the spine, and the extreme curve lets the knife cut in three directions from a single handle position, whether pushing the blade forward, pulling toward the user, or pressing down. A fillet knife can cut in different directions but has the blade really thin so the user can turn the knife with a minimal turn radius to change the direction of the cut. /EDIT

What this leads me to think is that we may perceive our design optimizations to be well reasoned and objective, but that perception of objectivity is illusory. Completely different teams approaching the problem with a blank slate are likely to come up with unrecognizably different solutions to the problem, even when adhering to basic design requirements like using a blade and having a handle. You might think that radically different techniques get employed for the use of each of these blades, but after watching videos of each of these blades being used by competent fishmongers, I don't see a lot of difference. All the differences in technique are subtle at best.

If you showed the blade smiths who designed each of these radically different fish filleting knives the fillet knives produced by the other two traditions, and asked them to guess the function and purpose of the other knives, would they even be able to guess the function correctly?

If I had not seen the Taiwanese style knife being used to fillet fish, I would never guest that the spade-like shape was intended for cutting fish. That shape is broad to the extreme in the same way that the western fillet knife is thin to the extreme. Same with my first impression of the deba.

Greenhill Forge, The same projects channel that brought you the comparison of various methods for doing solar air heating is now doing the same sort of comparison and analysis of various methods for doing solar water heating on a DIY basis.

In several of the things I want to model in FreeCAD, I need to model curves like parabolas and hyperbolas while also having access to the focus point. In another project of mine, I need to model an involute for a special cam, and in yet another, I need to be able to model epicycloids and hypocycloids for the rotors of a multi-lobe blower.

How would I go about modeling such curves in FreeCAD? I would prefer not to have to use a bunch of splines to try to approximate these shapes.

At every market where I’ve seen them, English cucumbers are shrink wrapped in plastic. No other cucumbers are wrapped like this. Why?

What transit looks like if not dominated by the automobile industrial complex.

Recent breakthroughs in sodium battery tech are taking sodium batteries mainstream. Sodium is one of the most abundant elements on the surface of the earth, but it also has other extremely compelling advantages over lithium batteries for grid power storage: it doesn't require a narrow temperature range to maintain its operations, and it is much easier to gauge the state of charge on sodium batteries.

Right now, sodium batteries are only beginning to be mass produced. In the battery industry, the prices of batteries drops about 19% every time manufacturing volume doubles. Sodium batteries are already cost-comparable to lithium batteries, so as manufacturing scales up, the prices are expect to drop far below that of lithium batteries. The biggest implication of this development is that renewable energy made in excess of immediate demand no longer needs to be curtailed or dumped. Unlimited inexpensive sodium batteries means all this energy can be inexpensively stored. And once renewable energy can be inexpensively stored, all of the arguments against the adoption of intermittent renewable energy sources (such as solar and wind) become outdated and irrelevant.

In Germany, a substantial amount of solar power adoption has come from apartment dwellers buying photovoltaic panels that they mount on their balconies, directly running the wires into their homes. Now, with plug-in home battery backup systems proliferating, solar power can charge these batteries up with enough energy to run all night, enabling this combined solution to provide enough energy to take some of the most energy-intensive appliances completely off-grid, and off the electricity bill.

Unfortunately, it is not always legal to do this elsewhere.

I saw this in my YouTube feed today. There is more public awareness of Solarpunk each time one of these videos gets made.

Greenhill Forge is a pretty neat channel. The channel has a bunch of projects for renewable energy, off-grid living, homesteading, etc.

The prior video in this series tested five different solar air heater designs, and settled on a variation of the best performing design from the test for this project.

My one gripe about this project is that the insulation is polystyrene, and the expanding foam adhesive is polyurethane foam, and cutting this foam produces crumbs of plastic foam waste. Material selection could be optimized further for sustainability, but over-all, the amount of power saved by using a solar air heater to dry clothes is very impressive. The only remaining power usage was to power the two fans (the large PC fan for the air heater and the fan that blows hot air into the dryer) and the motor that tumbles the clothes, plus the control electronics. 155W can be handled by a decent sized PV panel on a sunny day.

The solar air heater's biggest use-case is to warm up a home on cold mornings without requiring the use of fuel. The dryer is interesting but isn't the best use of such a device.

On another note, the word "trillionaire" gets flagged as a misspelled word. It doesn't even seem conceivable to spell check that this is a word; who could have imagined that it would be possible to be a trillionaire? A person would have to increase their wealth by a million dollars per year for a million years to have a net worth of a trillion dollars.

Any executive dumb enough to think they could get AI services for free is dumb enough to be replaced by an AI. Even with high fees, replacing dumb executives with AI agents would probably cost less than what they pay executives nowadays. I bet they never thought about that.