Distance per volume (mpg or km/L) is kind of a lousy way to reason about fuel economy; a better system is to take the reciprocal: gallons per mile, or liters per km.
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Paul Cantrellreplied to Paul Cantrell last edited by [email protected]
Is this just one of those Weird Unit Things where you can’t really picture it? Or is there actually some reasonable physical interpretation?
Turns out: yes, the latter! Imagine that area mounted to the front of the vehicle. The volume it sweeps out as the vehicle moves is on average the volume of fuel it uses.
Is this an even more useful way of thinking about fuel economy? No!
But it’s fun.
2/2
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@inthehands have you seen the cursed units videos?
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@kmccoy
I have not, but I hope I am about to! -
@inthehands this was the subject of one of the earliest XKCD what-ifs!
https://what-if.xkcd.com/11/ -
Stan ILWU ✊ :Schwerified:replied to Paul Cantrell last edited by
There are a lot of very weird units, when you stare to hard at them. For example, the Hubble Constant is (70 km/s)/Mpc -- that is, a speed per Megaparsec, which checks out. but the distances technically cancel out, so the result is a *frequency.*
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Stan ILWU ✊ :Schwerified:replied to Stan ILWU ✊ :Schwerified: last edited by
I'd make the case that it's not really the same "distance" being cancelled out. even though they're both the same kind of unit, one is a distance related to the galaxy's motion and the other is a distance *to* the galaxy.
I think the same reasoning would apply for the lengths composing fuel volume and the distance of a car traveled.
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Paul Cantrellreplied to Stan ILWU ✊ :Schwerified: last edited by
@thedansimonson
You’re the second reply to mention that video!I hear your argument about lengths coming from different places, but…dimensional analysis doesn’t care. And per my 2nd post (and the video), there is in fact a perfectly reasonable physical interpretation that units the lengths.
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@kmccoy
Good stuff! -
@inthehands You probably already know that in Germany and neighbouring countries (perhaps elsewhere in Europe too), it is common to measure "liters per 100 kms".