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xkcd #3038: Uncanceled Units (xkcd.com)

submitted 5 days ago* (last edited 5 days ago) by [email protected] to c/xkcd

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Edit: Alt Text: Speed limit c arcminutes^2 per steradian.

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[–] trxxruraxvr -1 points 4 days ago (6 children)

My point is that kWh is the same. It doesn't say anything about time. 1 kWh is 3.6 MJ. There is no difference except the factor 3.6.

[–] blackbelt352 1 points 3 days ago (5 children)

The important thing is that leaving units uncanceled is a valid way to communicate the relevant factors of what a number represents.

Yes technically kWh cancels down to joules, but that doesn't communicate the relevant info of how a device uses that energy during a period of time. In other words Work (Watts) multiplied by Time (hours).

Uranium has 2x10¹³ joules of energy stored. You can use all that energy at once in a bomb and explode a city in a second, a lot of Work done very quickly, ooooor you could put it into a reactor and power a city and do a lot of Work during a much longer time period.

[–] trxxruraxvr 1 points 3 days ago (4 children)

Uranium has 2x10¹³ joules of energy stored. You can use all that energy at once in a bomb and explode a city in a second, a lot of Work done very quickly, ooooor you could put it into a reactor and power a city and do a lot of Work during a much longer time period.

And the amount of kWh provided is the same in either case. So using kWh gives you no relevant information about how the device uses that energy during a period of time.

[–] blackbelt352 0 points 3 days ago (1 children)

It definitely does provide information as my 50 watt lightbulb will run for an absurd number of years when hooked up to a nuclear generator and will be completely vaporized by the nuclear bomb.

Also keep in mind your average person likely doesn't remember their physics classes and how joules, time, and watts all relate to each other and that introducing new names to something just creates more confusion and headache and dumbasses phoning into their electric companies about how "my lightbulbs don't take joules they take watts and why am I paying for joules when I want watts."

kWh conveys the relevant information without introducing other names that can create confusion among the stupidest and most karen-like people you know.

[–] trxxruraxvr 1 points 2 days ago (1 children)

my 50 watt lightbulb will run for an absurd number of years when hooked up to a nuclear generator and will be completely vaporized by the nuclear bomb.

That is true whether you express the energy as kWh or MJ.

Also keep in mind your average person likely doesn’t remember their physics classes and how joules, time, and watts all relate to each other

It's becoming clear to me that you don't either. KW is not the same as kWh, the latter does not have a time component anymore despite the name. Watt is the amount of joules per second. kWh is the amount of energy spend it you use 1KW for an hour regardless of the time that amount of energy is spend in similar to how a lightyear is the distance that light travels in a year regardless of how long you take to travel that far.

[–] blackbelt352 0 points 2 days ago (1 children)

So a lightyear is an acceptable non-cancelation of units [(m/s)*year] but kilowatt hours [(j/s)*s] isnt. Got it.

[–] trxxruraxvr 1 points 2 days ago

Glad to see reading comprehension is at an all time high.

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