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by bovine3dom 2858 days ago
> And how much energy is in one Coulomb. The example I like is two points each with one Coulomb repel with a force of one millions tons.

Coulombs and therefore their related units such as Farads are famous in Physics for being far too large, so this is not particularly surprising (assuming a sane distance). The capacitance of the largest capacitor bank in the world is about 0.2 Farads [1].

[1] https://www.quora.com/How-many-Farads-does-the-largest-capac...
2 comments
photojosh 2858 days ago
This is a 1.0 F capacitor [0], we use similar ones for short-term UPS backup so our embedded systems can shut down safely.

And a Coulomb is one amp for one second, that's not exactly large either.

So it's not that coulombs and amps are too large a unit, it's that it's hard to convert and store large amounts of energy.

[0] https://au.rs-online.com/web/p/products/7898012/

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bovine3dom 2858 days ago
> hard to convert and store large amounts of energy.

Which I would say means that it's a bad unit. How about an amp for a nanosecond? That would lead to much more sensible numbers elsewhere.

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ericpauley 2858 days ago
Keep in mind that capacitance and capacity are not the same. Case in point, the capacitor mentioned can hold a peak voltage of 24kV, which is allows for a million times more energy to be stored than the same capacitance at 24V peak. Capacitors with far lower peak voltages can have capacitance exceeding several Farads.
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bovine3dom 2858 days ago
Yeah, I was taking some liberties with the definition of largest.

They're still a ridiculously big unit though. Generally the biggest man-made structures on Earth are measured in mega*. Single digits are usually used for things that are roughly apple-sized.

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photojosh 2858 days ago
But in electricity/electronics, we deal with the entire range of metric prefixes… terabytes, nanofarads, gigaohms, microseconds.

I'm curious as to what you mean by "biggest man-made structures" though. For me that brings to mind tall buildings, long walls and big dams. I suppose that the Great Wall is 20 "megametres" long, but normally long dimensions will be in kilometres, heights are in 100s of metres and dams are in billions of cubic metres. Care to share some examples?

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bovine3dom 2858 days ago
> But in electricity/electronics, we deal with the entire range of metric prefixes… terabytes, nanofarads, gigaohms, microseconds

But you don't. You'll almost never use whole Farads, for example. It's even on the Wikipedia page: related units, nF, uF.

> Care to share some examples?

I don't really mind the difference between giga/mega/kilo. I was really just talking about a ballpark where we don't want the biggest thing ever to be unity in our everyday unit.

You do raise a valid point with height. This is because the gravitational field in some sense makes length directional: 3km up is very different to 3km along. Clearly, we need some vector based measures so we could scale them sensibly, g-hat and x-hat : ).

Can you think of many man made structures who have just one of some extensive property in an everyday unit?

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