[Greenbuilding] energy and power terms

[nick pine]

David Bergman writes:

>The article also says, btw, that watts are comparable to horsepower. But I 
>do find their explanation before that rather confusing: "A laborer working 
>through the day will put out 75 watts of power. A medium-sized car might 
>consume 100,000 watts." Those sound like energy totals, not flows.,

Perhaps the intent was to say that the laborer can generate 75 watts for a 
long time, vs 300 watts for a shorter time. And accelerating a 4000 pound 
car from 0 to 60 mph takes about 1/2mV^2 = 1/2x4000x0.454lb/kg(60x0.447)^2 = 
653K joules. If that happens in 6 seconds, it might require a constant 
653K/6 = 109K joules per second, ie 109 kW for 6 seconds, or perhaps more 
power and smoke at the beginning and less at the end, at a non-constant 
rate.

Nick Pyner wrote:

>... If you must use automotive terms, I submit it might be better to use 
>the fuel gauge than the speedo.

The rate of change of the fuel gauge is closer to power than the speedo.

>Or how about the engine? A watt is exactly like a horsepower, just 3/4 the 
>size, and most of the world uses just that.

One horsepower is about 3/4 of a kilowatt, like 10 75-watt people.

Nick