CanadaPlus

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A backup account for !CanadaPlus, and formerly /u/CanadaPlus101 on Reddit.

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CanadaPlus ,

It’s a bit oversimplified, actually. Sound bounces off of discontinuities in the medium, which is why foam works. You just have to control scattering somehow.

The big problem with using oobleck or whatever is it responds to shear, and shear can’t travel through air. You could use it for earthquake protection, though, or if you could channel compressive waves from the air into shear form using a fancy bridge like in OP.

Also, shear-thinning fluid is a thing too.

CanadaPlus ,

Yeah, OP didn’t even phrase it like nobody else could have thought of it, which is a frequent pitfall for these kinds of questions. The experts that can give the best answers hate that. It’s implicitly saying their years of study aren’t worth much.

Is the "Tromatz" bioelectric wave toothbrush legit, or snake oil?

I discovered the “Tromatz” bioelectric wave toothbrush, and it sounds too good to be true, which usually means… it is. However, they do link to some journal articles, so it seems it’s somewhat based on fact. There’s very, very little else out there aside from their own website that I can find. Thoughts from anyone...

CanadaPlus , (edited )

Based just on the name even, snake oil. WTF is a “bioelectric wave”?

CanadaPlus ,

I think it’s like a third of an atmosphere or something. Enough to comfortably achieve the same partial pressure of oxygen as normal Earth air, by providing it pure.

CanadaPlus , (edited )

… That’s actually a good point. I’m guessing since the digestive tract is flexible and isn’t held open to the outside all the time, it wouldn’t cause problems with things deep inside. I also think it’s inevitable that if you did shit yourself in it, suction would kick in at some point and make it all a bit more dramatic. And then it would boil-freeze off into space, and be icy cold. That might still be better than pooping a sealed space suit, though.

CanadaPlus ,

In terms of engineering, it does. Micro meteorite protection and heat management can both be provided by normal garments. UV protection is obviously easy enough too. Breathing gas is a bit less convenient, but still not as tricky as making a suit that’s both rigid enough to reliably hold several PSI in and flexible enough to comfortably work in. That’s why the elastic suits are being researched like they are.

Why are we so concerned with oxygen production yet we never hear about nitrogen production, though we actually need 78% nitrogen vs 21% oxygen to survive?

Excess oxygen is actually harmful to humans, but all the climate warnings are about losing oxygen, not nitrogen edit: but when we look for habitable planets, our focus is ‘oxygen rich atmosphere’, not ‘nitrogen rich’, and in medical settings, we’re always concerned about low oxygen, not nitrogen....

CanadaPlus , (edited )

Atmospheric nitrogen is useless to most life, as it’s extremely hard to break down into other nitrogen compounds. Certain bacteria are the exception, and they’re very important both to ecology and human agriculture (although less so since the Haber process was invented and artificial fertilisers became available). The other natural source of nitrogen compounds is lightning strikes.

Oxygen is completely the opposite. It’s unstable in an Earth-like environment (which is why fires happen), and if you find it in such an environment there must be something special producing it continuously. It’s not the only biomarker astronomers look for, either. There was a planet with insane amounts of a chemical called DMS found recently, and that’s just as eye-catching, if weirder.

Deep sea divers also use a nitrogen mix (nitrox) to stay alive and help prevent the bends

You’ve actually got that somewhat backwards. To go really deep you switch to heliox or similar. Nitrox is for intermediate depths where you need less oxygen than in the normal nitrogen-oxygen atmosphere, but nitrogen narcosis isn’t an issue yet.

Why do many microwave ovens hum in an interval of a minor 7th?

Something that I’ve noticed across most of the microwave ovens that I’ve used is that when they hum while cooking food, I can pick out 2 distinct tones. One of them is pretty clearly 60 120 hz, the 2nd harmonic of the AC power frequency. The other is consistently a minor 7th above that (which would be somewhere around...

CanadaPlus ,

Wow. This question is a good but very specific observation, and I did not expect an actual answer.

Does everyone learn the same gravity in school or is it different everywhere?

So, I learned in physics class at school in the UK that the value of acceleration due to gravity is a constant called g and that it was 9.81m/s^2. I knew that this value is not a true constant as it is affected by terrain and location. However I didn’t know that it can be so significantly different as to be 9.776 m/s^2 in...

CanadaPlus ,

Newtonian physics also has gravity decreasing with height, no need to get out the big guns.

CanadaPlus ,

Is that so? I wonder what the story behind that is. Maybe it’s a surface average?

Most people would probably guess this, but meters and seconds are defined independently of Earth’s gravity, so it doesn’t have a true value, just apparently a standard nominal one.

CanadaPlus , (edited )

F=Gm1m2/r^2^

G is the gravitational constant, the m’s are the masses in question, and F is the force generated. The r is radius from the center of one body to the other; that is, height. If it didn’t decrease, orbits wouldn’t exist the same way and astronomers would have laughed Newton out of the room.

I could give you a link if you really want, but it’s the Newtonian gravity equation, so it’s probably just going to be “Gravity” on Wikipedia.

CanadaPlus , (edited )

G is also fixed in GR, although it’s not guaranteed to manifest in a neat relation like that in every situation because spacetime curvature has a lot of components at every point, and they interact super nonlinearly.

CanadaPlus ,

It also depends on latitude, and local geology and…

Maybe it is just weighted by surface area, you’re right, and that’s what I meant by “surface average”.

CanadaPlus , (edited )

No, it’s not worth it. Honestly that’s great all on it’s own. I guess they never had a reason to update it, then, since anybody that needs a more accurate value would just measure it themselves.

It looks like they went back to the original litre definition a few decades later. I’m not sure why they thought defining volume by mass rather than geometry was better in 1901, anyway. Some fun facts about the kilogram itself, since I never get to talk about this stuff:

Since 2019 the kilogram has been based on a “Kibble balance”, which is a contraption that precisely measures the force produced by electromagnetism. The necessary electricity is provided by circuit with a material that has quantised resistance near absolute zero, and a superconducting junction which produces oscillation exactly tied to the current flowing through, which is itself timed by atomic clock. This allows you to measure it out using just the new fixed value of Plank’s constant.

Before 2019 there was just a chunk of metal the was the kilogram, which is hilariously low-tech.

[Solved] Trees supposedly take 30 years *before* they absorb CO₂. Why?

I often hear science-adjacent folks stating that a tree needs to be 30 years old before it starts absorbing CO₂, usually paired with the statement that it’s therefore pointless to start planting tons of trees now for slowing climate change....

CanadaPlus , (edited )

Young trees of many species also grow faster, though, and if the old tree dies and decays all that carbon returns to circulation. Forestry, done right, actually is carbon negative. However, it’s also incompatible with the critters that need old-growth forests (and old growth itself soaks up carbon fairly slowly). Environmentalism needs to get better at appreciating tradeoffs IMO.

CanadaPlus ,

Depends entirely on species.

CanadaPlus , (edited )

Fun fact, cryonics came to prominence because it just works on small animals like mice. There was literally guys “killing” and reviving mice in the 50’s.

It’s entirely likely that the only barrier in humans is that we’re too big to quickly cool with any known technology.

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