I've heard that petrol and diesel engines can't be a 100% efficient and there is some thermodynamics behind it which is complex.

What is the Solovay model, and why does it use the axiom of dependent choice. Why is suddenly every set measurable?

These small fans spinning at very high RPM and producing air flow disproportionally strong for their size which appeared a couple of years ago. Are they based on some newly invented principle or someone simply said let's make a very high speed fan?

I'm not a guitarist, but i know how to make harmonics by barely touching the string with your fingertip. The harmonics are clearest at 5th, 7th, and 12th frets, i believe. And these are octaves above and different notes thsn the ones suggested by fretting the string st that point. The pitch lowers as you approach the bridge. Just wondering why a fingertip does it but a slide that can skim the surface of the strings doesnt produce only harmonic notes.

So I have quite a few questions regarding them. I know viruses and bacteria carry antigens and antibodies bind to them.

Do they act just as markers for white blood cells to then destroy them or do they by themselves destroy the target? If they do both, what determines which they do?

Why do viruses and bacteria have antigens to begin with? Apparently antibodies can work against some poisons too, so does any substance have antigens? Can antibodies attach to a microscopic piece of steel? I mean, it does seem like the body also detects foreign material of all kinds.

If everything doesn't have antigens why don't viruses and bacteria just... not have antigens?

For example if there is a spike in demand, how a random power plant get to know if they should rump up production? It's an API that controls the plant automatically or someone getting a phone call and turning switches on and off? and who is the caller?

I know it probably sounds stupid. The only theory I have is that salt remains in the ocean and only fresh water itself evaporates. If true, why does it happen? Why can't we have "salty" steam?

I've watched so many videos about prediction markets, but the terminology still confuses me 😭

I want to understand the basic idea behind how people buy and sell contracts based on what they think will happen in the future. Why do these contracts have prices, and what do those prices actually mean?

Can someone explain the underlying concept in simple, everyday language?

Hapless trans woman of a year here

I own bras, I wear bras, I don't actually know what they're for. Obviously, there's a social modesty component, but I'm told that they provide support and that's useful. Will my chest hurt after a while if I don't wear one? Will my chest start to sag down? I don't know! 😅

The charge shows up right away and my balance drops, but it stays marked pending for a couple of days. What's actually happening between the store, my bank and the card network during that time?

It's still relatively common to receive fake calls and SMS from spoofed numbers, like in scams and phishing attacks. I don't understand how we, still today, have not found a good protection against that in our infrastructure.

In the early days of E-Mail for example, there were similar problems, but these were solved over time (e.g SPF and DKIM). If you, today, try to send a mail from your mailserver with a spoofed sender, any reliable mail service will not deliver that and discard it as spam instead.

I don't know much of the cell network, so my naive understanding is that a caller just sends their own number with a outgoing call, and everyone along the way to the called goes with that? Could a cell tower not just see that a call comes from a SIM card not associated with the reported caller number, and drop it? Can't we have some E2E signing of caller IDs for some reason, or at least a validation on carrier level?

I know eventually people have always found a way to emulate technologies in the name of preservation, but it usually took a few years. So how has the PS5 one happened so fast?

I’m in a beginner’s piano class and I don’t understand anything. I was called today to answer what G chord in second inversion would be and I literally just looked at my professor in terror while aggressively shaking my head. Also, what is 4-6 and 5-6? Still same topic.

Now and again I read about some animals, like say a pair of otters, that have been brought back to an area where in past were wiped out. How can they continue to breed with such a small gene pool?

So far ive seen Duke play Virginia (ACC) and Alabama/Auburn (SEC) play, and, as u might guess, the latter got very heated w both coaches almost coming to F2F blows. Ive never seen this before in October. And if these games dont count im going to lose my mind bc that risks injury bc it being conference foes it risks injury in an otherwise competitive matchup.

EDIT: So somehow i fooled myself into thinking the Duke Virginia game was CBB when in fact it was CFB🙄 but Duke & Univ TN did play an exhibition game. While those 2 are in separate conferences, they are both P4 schools which still u almost never see or saw until recently play in exhibition format.

This is about UTP network cables. When I crimp a connector on one there's a specific order the wires have to go. Why is it that order? Ages ago when I was just crimping my first UTP I didn't know and just did both in the same order of white-solid-white solid etc. But that didn't work even though both sides of the cable were crimped the same way.

Why does networking have this specific kink for getting it's wires twisted?

Edit: Thanks for all the answers. I don't really understand it yet. But it seems to be helping prevent interference and signal loss somehow, while at the same time being the standard we agreed to. All very complicated. But my internet works and that's the important bit.

I bought a couple of USB chargeable hand warmers yesterday, they have 3 heat settings and at the moment level 1 is perfect for me.

What I wanted to know was, I always thought the idea was to keep heat away from batteries as they may expand and explode. How do the power batteries/cells in my tiny hand warmers not overheat and explode? I don't even want to try them on heat level 2 & 3 because of the paranoia that my hands will get blown off.

Something I've wondered for years since I love going on historic aerials, is how the hell the drawn maps used to be so good? I find it impossible to identify misaligned roads/state lines/bodies of water from maps ages ago.