xkcd #3038: Uncanceled Units
xkcd #3038: Uncanceled Units
Edit: Alt Text: Speed limit c arcminutes^2 per steradian.
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kWh is already an uncanceled unit, drives me nuts even without adding per day
(Energy / time) * time? fuck you
It's because the times aren't the same. Maybe same unit but different context so they can't be canceled.
It's like saying you work 8 Hours/day (Eight hours per day). Both are units of time, but their context is different and their combination forms a new meaning beyond the units.
1 KWh is using 1KW for one hour. Because of demand pricing the time you use that KW is important. Like in terms of energy grid using a whole ton of power for one minute vs same total over a long time is different and important dispite being the same amount of energy.
Edit: some phrasing
Time cancels out.
I work 8.
Gotta convert time to the same units before canceling: you work 1/3
Rough day today, I pulled 10 radians.
Good point, and agreed that thinking in kWh is very intuitive and convenient in some contexts like household appliances, but it's being used as a more general unit for energy while Joules are just so much better at, well, representing energy and being able to transition from electric to thermal etc.
I know why but it's stupid and arbitrary and the arbitraryness is what's forcing it.
It's the time. It's always the time.
SI units are all derived from seconds but instead of working with kiloseconds we have minutes and hours and days with a bunch of idiotic conversions.
The "second" you invite time into your measure, you invite some real bullshit ad-hoc pseudo-unit convenience units and fuck them. May as well just go imperial and have 14 rods to the fucking hogshead.
Is that a standard hog or a chefs hog?
Because nobody's used to seeing Joules, you could swap in kJ for kW-seconds but then you probably need to switch base (MJh) to keep it practical, and now people need to do extra math to tell what will be on their power bill
But go ahead and call your power company to get them to list Joules
My power company provides me electricity in kWh, and heating (in the form of hot water) in GJ. And my cold water gets charged in m3.
So they DO know. For a few years, they'd even "helpfully" translate the GJ into kWh, untill it started to piss off people who bought electric heaters and found that those two numbers weren't actually the same in the real world.
My power company DOES tell me in Joules, but only for gas so that's already bullshit, and I live in Alberta so people already can't decipher their fucking power bill's opaque energy/distribution fee/transmission fee costs so that's bullshit too
But ...we're human - bullshit is really all we've got.
I suppose there is science, but eww...
In the U.S., they meter gas by the "therm," which is defined as 100,000 BTUs. It's a misconception that it's equal to 100 cubic feet of natural gas at standard temperature and pressure, and is merely a coincidence that those values are very close.
BTUs are like a shitty imperial calorie, the energy it takes to heat up one pound of water by one degree fahrenheit.
Also, don't confuse therms for thermies, a totally different unit that means the amount of energy required to heat up a tonne (1000 kg) (not to be confused with the imperial ton that is 2000 pounds) of water by 1°C.
Energy is so useful in so many different contexts that we can just always expect a million ways to express it.
It's also due to social inertia.
Power companies charge by the kWh because their generators are measured in total output wattage and consumers consume at different wattages at different times.
Sure, it would be easier to measure in total joules consumed per period time but it would also be easier to measure with world standard metric units. The pain of changing is harder than staying the same, so muh freedum units.
It gets even better when you read about annual or even daily energy production of a specific power plant.
For example, the annual production of Aswan dam in Egypt is about 10 042 GWh, which translates to an average power output of about 1.1 GW. Now that you have this number, you can compare that with the maximum theoretical power output which is 2.1 GW. Therefore, they should have plenty of capacity left, but you can't tell that just by looking at the published numbers. They just have to use convoluted units, because that's the tradition in a bunch of industries.