Actually I’ve worked on a system similar to this. It’s a flywheel generator. Magnetic bearings, vacuum enclosure, 6ft diameter steel fly wheel. You spin it up really really fast, and it spins for years. There is some very slight energy input to counteract any loses, but it’s very minimal. But when you need power the fly wheel could power a house for a couple days (with the right inverter). Totally impractical but a cool prototype not work on.

Sleeping in the driver's seat also seems to be spreading around the US lately

Eh. I get your point but a 50hp minivan or a pickup with a family of four would slow as crap and sorta dangerous. I remember driving an old vw a few times and they would certainly get from point a to point b but they were pretty anemic. Part of this is just the enormous mass of modern vehicles. Let’s say more than 200hp is probably not necessary? But 400 is perfect

The fastest way to stop a car is to drive it into a wall. Also when you are braking with brakes you are already doing engine braking as well, since that takes place whenever you are in gear and not pressing on the accelerator.

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Hypothetically yes, engine breaking might* give you a small amount of additional breaking force.

In practicality you should focus only on slamming down the breaks as far as they'll ago (assuming you're driving a vaguely modern car). Fyi the breaks on a car go a lot further than most people ever try.

*Might not because the limiting factor could be how much traction your wheels get, at which point adding additional breaking via the engine won't help.

Check the paper I linked.

are you talking about harnessing the energy from this machine? Because t hat's the thing that is pointless. You can make something that ALMOST stays perpetually in motion but it cannot remain in motion as soon as you try to tap into that energy.

The planes with single engines in the vertical stabilizer are due to a law that required twin-engine aircraft to always be within 60 minutes of an airport.This regulation came to be known as ETOPS: Extended range Twin engine Operation Performance Standards. (Or, "Engines Turn Or Passengers Swim)

This law did not apply to jets with 3 or more engines. If carriers wanted to fly longer, over-water routes, they had to follow coastlines, or fly planes with more engines. It's cheaper to operate 3-engined aircraft than 4-engined, so the market made 3-engined aircraft.

Planes with an odd number of engines can't divide them between the wings; they need the odd one in the fuselage. It has to point aft, so the tail is the natural choice.

With improved jet engine reliability, ETOPS standards have been extended from 60 minutes to 120 minutes in 1985, and 180 minutes in 1988. Some twin-engine aircraft are now certified to fly up to 370 minutes from a diversion airport. The era of trijets is rapidly coming to a close.

If you are American then I assume you know about the mag stripe on the back. Think of chip cards as storing the same data as a mag stripe but it also changes the codes every use, and the previous codes can’t be used by your card again; this way even if someone gets that info, it’s useless. As for tap to pay (card or phone), it’s just a wireless version of the chip.

If you want to move something from A to B you do work: https://en.m.wikipedia.org/wiki/Work_(physics)

Now the question is how fast you want to do this, so work over time, this is power: https://en.m.wikipedia.org/wiki/Power_(physics)

So even though a car and a tractor might do the same work (going from A to B), a car does it much faster thus requiring more power.

So in simple terms: Going up 100 stairs slow and steady is not very exhausting but sprinting them as quick as you can leaves you exhausted and panting for air even though you ended up reaching the exact same goal.

So I didn’t know this was a thing, it kind of made me realize how bad my vision has gotten seeing the contrast

Australia has speed limits of 110km/h on the highways and far fewer deaths per capita than the USA. But we don't drive as many American cars and we're less drunk on the road.

I recall also often being able to choose between Ad Lib, Gravis Ultrasound, Roland MT-32, Tandy, and sometimes PC Speaker.

To explain how the apps work, we need to understand how chips and contactless cards work.

Credit and debit cards are essentially just reusable check blanks. Written on them, you have the account number of the person trying to send money and the name of the account holder. When using the card to buy something at a shop, the payment computer has the account of the ones receiving the money (the shop) pre-programmed into it, and the employee at the till has punched in the amount to be sent. This is basically all the necessary components of a check. The payment computer phones up the bank with this info to request a transaction, and if the bank computer responds, "Looks great, we'll get that sorted!" the payment goes through and the terminal shows it as paid.

The magnetic strip on older cards is more or less just the info printed on the card, digitized, so the sale computer can read it quickly and mistake-free. Swiping a card is, for layman's purposes, hardly different than just punching in the data printed on the physical by hand, with a magic spellchecker that can tell if you typo'd it.

Now, if that's all a credit card actually was, just a name and account number, it'd be very easy to steal. So they have security built into them to make sure that only the rightful owner is using them. Basically, give the cardholder a test to prove it's actually them.

The oldest (and stupidest) form of this is the signature. The idea is that the card holder writes their signature on the physical card. Then, when making a sale, the cardholder also signs the receipt. The cashier should take the card and receipt, look at the two, and only allow the sale if the two match. The hope here is that A) your signature always looks the same every time you write it and B) only you can write it the way you do, no one could ever copy it. So if the signatures match, you must be the cardholder.

A much better solution is a PIN. It's basically just a tiny password that only the cardholder should know. If someone steals the card (or even just the numbers on the card), but do not know the tiny password, they can't use the card.

This idea is taken to the next level with a chip. In addition to giving you a PIN to memorize, the credit card company makes two identical copies of a tiny computer. One gets embedded into your card, and they keep the other. When you attach wires to this tiny computer and power it on (which is what inserting your chip into a chip reader actually does), you can send it some gibberish data, and it will answer back with more seemingly unrelated gibberish data. The key, though, is that every time you ask it the same gibberish question, it replies back with the same gibberish answer. So, when you insert the chip into a chip reader when making a sale, the card network can come up with a gibberish question, send it to your card's chip, and get the gibberish response back. It then asks the same gibberish question to the copy they have on hand. If the answers are the same, it must mean you have the chip, and by extension you must also have the physical card.

The beauty of the chip solution is that even if an eavesdropper somehow was listening to the conversation between the card company and the chip, and they overhear the gibberish question and answer, it's useless to them. That's because even if they technically know the "answer" to one of the gibberish questions, the card company will never ask that question again. All questions are single-use, and thus so are all answers. The only way to truly spoof the card is to be able to know every possible answer to every possible question. Or in other words, physically have the chip. So the chip effectively defends against people who know your numbers, but haven't physically stolen the card. A PIN is still required to defend against physical card theft.

Contactless tap is basically the same as chip, just done over radio waves instead of wires. This makes it easier to eavesdrop, but as we established already, eavesdropping on a chip payment isn't all that helpful to a thief, so we don't really care about that!

Now, finally, the payment apps. When you install a payment app and register a card to it, what you are essentially doing is turning your phone/watch/whatever into a credit card chip. The credit card company creates a secret program that works like a chip--takes a gibberish question in, gives a gibberish answer back--and installs a copy of it to your device. So when you tap your device to the reader, it gets asked a gibberish question, it creates a gibberish answer, and radios it back to the terminal, just like a chip. This proves that you have the physical device. It doesn't prove you have the physical card, but registering the card in the app in the first place did prove that you must have had it at some point, which is good enough.

There have in fact been at least two planes designed in the last decade (or so) with an engine in the vertical stabilizer

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If the speed doubles and the force required quadruples, then the power goes up by a factor of eight. This is because power is proportional to force times speed.

The above is true for air resistance and water resistance, where drag is proportional to speed squared. I found a publication linked in this thread that says the same is true of plowing, but another commenter found a paper with experimental results showing the force required increasing much more slowly with speed. If so, plowing is not like fluid resistance and the power required increases even less than the square of the speed.

I came here looking for this comment. Thank you sir.

Sort of. A true pinhole camera creates an image that is already 100% focused. The bigger the hole (“aperture”), the wider range of angles the light is coming in at, and the blurrier it gets without additional focus. (It’s not “noise,” it’s the wrong signal.) Think of holding up a piece of paper, take a little square on it, and imagine where the light comes from that hits that square. If there is no pinhole at all, and it’s just open to the environment, the light that hits that square is coming from all directions and you just see white. If you block out all but a medium sized hole, the light can only come from the direction of the hole, but there are still several possibilities for its source which get mixed together in a blur. Once you shrink down to an infinitely tiny hole, the light hitting any spot on the paper can only come exactly from the direction of one point on the other side of the hole. Repeat for every other point on the paper, and it’s in focus and you get a picture.

The problem is that an infinitely small hole lets in no light. And the wider the hole, the more possible angles that light can come in at, and the blurrier it gets. That’s where lenses or refractive mirrors come in, but OP didn’t ask about that…

>So the only way to make something "run for a long time" as a power source is to really really slowy take energy away from it. Why would we bother to do that?

I agree with everything you're saying, but there are some fairly obvious answers to this question, because there are plenty of things that require very little power but that are difficult or impossible to service and thus you want to last a very long time - pacemakers, for example, or certain robots designed for space that use very low power, very long lasting nuclear power sources.

speed limits generally max out around 70 screaming in German

How is washboarding a concern on a field that's being plowed?

Me too buddy. It sucks.

That's not the whole truth though, a lot of cars also need the speed, e.g. police and emergency vehicles.

The maximum speed limit is also higher than in the US in basically every country.

In Most European countries it's around 80 mph (130 km/h) and then there's Germany of course. For me as a German it is pure hell to go only 130 km/h on a straight road with no obstacles and low traffic. Feels super dangerous because you will get bored and "fall asleep" very fast. I guess that's how Americans manage to produce so many accidents on their highways despite the low speed.