huhuhu ^_^

"TheCroatianGuy" (TheCroatianGuy) 09/14/2014 at 09:04 • Filed to: None

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Cé hé sin > TheCroatianGuy 09/14/2014 at 09:36

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Isn't 2 bar actually twice atmospheric pressure, not pressure plus twice the pressure as the caption suggests?

PS9 > Cé hé sin 09/14/2014 at 09:40

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I don't really read 'exceeds by' as '+'

Cé hé sin > PS9 09/14/2014 at 09:42

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I do though. It could more usefully read "equals twice atmospheric pressure".

vdub_nut: scooter snob > Cé hé sin 09/14/2014 at 09:46

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no, because it's already at atmospheric pressure when the tire is put on. 29 psi is really "29 psi more than the outside air" in this case.

Cé hé sin > vdub_nut: scooter snob 09/14/2014 at 09:49

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Oh, that makes sense now I think about it. A tyre at 1 bar would be flat.

The Transporter > Cé hé sin 09/14/2014 at 09:55

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Both of them are actually wrong, but everyone uses this convention because sometimes it's easier for everyone to agree upon a short lie than to tell a more complex truth. When we say that there's no air in the tire, we are clearly lying to ourselves and everyone else because if there was absolutely no air in the tire there would be a vacuum in the tire and the tire would have collapsed in on itself. What we mean to say is that the tire has no air in it over the ambient atmospheric pressure of approximately 14.7 PSI or 1013 milibars . But that's a mouthful to say every time your tire goes flat, especially because you're already frustrated by the fact that your tire is flat, so we chop off the last half of that sentence for brevity's sake.

So both of the graphic's statements are wrong in the strictest sense, but they are correct according to the standard agreed upon lie.

Jayhawk Jake > TheCroatianGuy 09/14/2014 at 09:57

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I always roll my eyes at metric vs imperial units stuff.

I'm an American engineer. Does metric make more sense? Yes, kind of. Everything is a factor of 10, that's nice. Bar is a decent way of measuring things I guess. Kilos makes more sense than pounds I suppose since it's a mass.

But I grew up on imperial. I know what a foot is, I know what a pound is, I know what an inch is, I understand psi. Obviously it would be different if I grew up in Europe, but I didn't. You'll never convert me to metric because imperial is natural to me.

Cé hé sin > Jayhawk Jake 09/14/2014 at 10:03

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Whatever about the general public, do engineers actually work in Imperial units in the US? Do people still use 5/16 inch nuts and bolts or whatever?

Jayhawk Jake > Cé hé sin 09/14/2014 at 10:14

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Yes. In aviation it's all we use. Well, at least American/British aviation. I think Airbus and Bombardier do too, but I'm not certain.

I worked on wind turbines for a while, we used metric.

Renescent > TheCroatianGuy 09/14/2014 at 10:22

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I conceptually understand this... now that that is out of the way, I'll admit it messes with me every time I use the power air pump that came with my Merc. I use it for everything from basketballs to bike tires to my lawn tractor.

vdub_nut: scooter snob > Cé hé sin 09/14/2014 at 10:23

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Would a pressure gauge not hooked up to anything read 1 bar or 0 bar?

(I genuinely do not know, and that may just be how they make them if it gives a misleading answer)

DoYouEvenShift > Jayhawk Jake 09/14/2014 at 10:24

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I think thats what it comes down to really. I know what 100 degrees fahrenheit feels like, just like a person that grew up in Europe knows what 37 degrees celsius feels like.

Cé hé sin > vdub_nut: scooter snob 09/14/2014 at 10:30

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0 because they read pressure above atmospheric.

norskracer98-ExploringTheOutback > DoYouEvenShift 09/14/2014 at 10:33

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Everybody knows what 37 degrees celcius feels like. (Body temp)