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Comment by iampivot | Hacker News Reader

I'd assume they'd worry more about the daily 450 degrees temperature more.

Might be cooler at the poles.

Just to clarify for anyone wondering: that’s 450C or over 850F. And the atmospheric pressure is about 93 bar, which is 4 times the pressure inside the boiler of a steam engine.

> 93 bar, which is 4 times the pressure inside the boiler of a steam engine

Or it is 93x atmospheric pressure, which is what 'bar' indicates...

I’m one of those people who was ignorant as to what ‘bar’ indicates. Now I know, but there’s nothing wrong with the steam engine example for imagining a comparison.

I suppose I think a bit differently. I don't know the typical pressure inside a steam engine. However, I do know what one bar, or one pascal means.

I can also guess what ninety atmospheres entails in terms of engineering, because I know that's the pressure at about 900 m water depth (by virtue of the SI units, which are based off water: P = hρg), which few submarines can even reach.

The same thing goes for 'as long as/as big as xxx football fields': which one? American or association? I know what a square metre is, I know what a square kilometre is, just use the damn units.

I really think pop-sci and science education should emphasise standard units (read: SI, not USC) and being able to estimate orders of magnitude.

You don't need to know the typical pressure , but you definitely get the idea the pressure built inside a steam engine is much higher than atm.

The steam pressure is not about the numbers so much but a kind of hyperbole , "you know that thing which hauls tonnes of steel purely on pressure made in a steam boiler , yeah the pressure on Venus is 4 times that pressure "

I found it an interesting fact.

> a kind of hyperbole

I didn’t think of it that way initially, but this makes sense, thanks.

Why reference submarines? What submarines can reach is irrelevant as a comparison when you know a number

Otherwise, it's your reference to submarines that contextualizes the number, same as the insides of a steam engine does for others

> it's your reference to submarines that contextualizes the number

I realised that after the fact. What I meant to say is that standard units should be used, and individuals should be left to contextualise said units of their own accord, instead of it being done for them.

Or both, numbers plus example don’t take much space.

Pedantic: 1 atm = 1.01325 bar (exactly). They're nearly equivalent units, even more so when you consider that Earth's atmosphere varies by more than 1.325% on a given day. But in a strict sense they're not the same.

A variation on the survey foot.

The US survey foot, as you probably know having brought it up but elaborating for the audience, is the old US foot before it was averaged with the British foot to create the international foot. It is 500000/499999 international feet.

Insert the obligatory "Americans will measure in anything but metric units" joke :)

I’m actually Canadian. I like that joke because I think a lot of units are useful for calculations but completely unintuitive. If I had instead said it was 9.3 megapascals and left it at that it wouldn’t have given most readers an intuition for how much pressure that really is. The pressure inside a steam engine boiler comparison, while not perfect, gives a bit better frame of reference because people have some intuition for how powerful steam engines are.

Oh and I like the unit ‘bar’ because it’s the customary unit for espresso machine pressure (and I’m an espresso nerd with my own machine at home). Espresso machines make espresso by forcing hot water through a puck of finely ground coffee at a pressure between 8 and 12 bar. If you’ve ever worked with an espresso machine, you’ll have an intuitive sense for how much pressure that is (a lot). Venus having 10 times that pressure is also impressive.

I like measurements that are immediate and visual. Your comparison to boiler pressure was a perfect example of that (I also immediately imagined the boiler blowing up :) )

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