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Comment by retrac | Hacker News Reader

Most here probably won't need this but: the Watt is a unit of power. Power is the rate of energy consumption. An amount of energy, over an amount of time. 1 Watt is 1 Joule per second. The "over time" is literal: 1 W = 1 J/s = 1 V*A/s. 1 watt, is 1 joule per second, is 1 volt-ampere per second.

An analogy to motion: joules are distance, watts are speed, and watt-hours are like light-years.

The amount of energy consumed, if you have one watt of power for a certain amount of time, is the confusingly-named Watt-hour, or Watt-year, etc. 1 Watt-second is 1 Joule. 1 Watt-minute is 60 J. 1 Watt-hour is 3600 J.

I'm not really sure why the Wh exists, other than to let you easily estimate how much it costs to run an appliance for once hour. It tends to confuse.

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> I'm not really sure why the Wh exists

It never really clicked for me how silly this is until you said it, so I went and looked it up.

It turns out it's kind of the other way around; the watt came first: It was originally defined as "the power conveyed by a current of an Ampère through the difference of potential of a Volt".

Watt-hour seems to come around in the 1890s as utilities explore ways to bill customers for electricity use, originally "ampere-hour meters" and then "watt-hour meters".

Joule shows up about the same time, in like 1880 or so, and was defined in terms of the watt, rather than the watt defined in terms of the joule, if I skim Wikipedia correctly.. So that'd mean Joule and Wh are both kind of competing units of energy - one used by GE and Westinghouse and all those people, and the other used by scientists(?)

The watt then gets redefined in terms of a joule much later, in 1948.

> Watt-hour seems to come around in the 1890s as utilities explore ways to bill customers for electricity use

Makes sense kwh is an accounting unit of energy not a science unit. I feel that's 'fine'. Tell the accountant that the pump that drains the east shaft runs 12 hours a day at 53kw and they can figure the monthly cost using a ten key.

Hat tip the parent. It's really annoying that Journalists understand neither science nor accounting.

> 1 W = 1 J/s = 1 V*A/s

That last "/s" should not be there.

it's a nice human scale unit - a bit like some countries still cling to inches as a length measure.

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