Watt Hour
- Thread starter chris kennedy
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Just last week, on the show "Are you smarter than a 5th grader", they asked the question:
"How many watts are in a kilowatt-hour?"
They said the correct answer is 1000. If that is correct, then there are also 1000 watts in a kilowatt-second, and 1000 watts in a kilowatt year.
The question was kind of like asking how many feet are in 1000 cubic feet. They are different things.
Steve
"How many watts are in a kilowatt-hour?"
They said the correct answer is 1000. If that is correct, then there are also 1000 watts in a kilowatt-second, and 1000 watts in a kilowatt year.
The question was kind of like asking how many feet are in 1000 cubic feet. They are different things.
Steve
eric stromberg
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tallguy said:
Yeah, but that only works on unsuspecting Romulans
LarryFine
Master Electrician Electric Contractor Richmond VA
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Wouldn't the rate of change in power be what/hours per hour, like 32 ft/sec per sec?rattus said:
Or is that what "watts/hour x hours" means?
rattus said:
Just to be a jerk, :grin: it would actually be a velocity of power, if the whole (displacement, velocity, acceleration) analogy holds. "Watts/hour" would be a function of the first derivative of power. It would be the second derivative of energy; i.e., an acceleration of energy.
Sorry...I just had to take the shot. I don't get to catch Rattus being wrong (even slightly) very often.
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No, it would just be watts per hour (or it can be written as watts/hour). But then, it still has no useful application.LarryFine said:
Think of a large industrial complex, perhaps one with lots of very large furnaces, perhaps a foundry. Consider bringing it on line from a dead cold condition. You don’t turn everything on at once and expect to get everything immediately up to full temperature. Things slowly heat up, and the amount of energy drawn by the building slowly gets higher. You can measure the amount of power (watts) being drawn at the end of the first hour, and measure it again at the end of each subsequent hour. Suppose you measure 5 watts at the end of the first hour, 15 watts at the end of the second hour, 25 watts at the end of the third hour, and 35 watts at the end of the fourth hour. Each hour, the building draws 10 watts more than it did the previous hour. The power being drawn at the end of the fourth hour is 35 watts; the rate of increase in power is 10 watts per hour.
How often do we care how fast a building is increasing power from zero to its full rating?
We should drop the notion (and the notation) of watts/hour out the window, and never look to see where it falls. :wink:
Nope:
Nope:
Power is the first derivative of energy with respect to time--the analog of velocity.
The second derivative of power with respect to time carries the units of watts/hour or joules/second^2--the analog of acceleration.
Here we have the same math describing different physical quantities.
Nope:
bcorbin said:
Power is the first derivative of energy with respect to time--the analog of velocity.
The second derivative of power with respect to time carries the units of watts/hour or joules/second^2--the analog of acceleration.
Here we have the same math describing different physical quantities.
rattus said:
Yeah, I would agree. Watts/hour (watts per hour) would be a strange term to use. It woud imply a device that increased its power usage as time went along. So If I had a hair dryer that had a Watts/hour rating of 200 Watts/hour... then assuming I turned it on at 5 pm and kept it on until 9 pm... at 5 pm it would be using 1200 watts, and 6 pm it would be using 1400 watts, at 7 pm it would be using 1600 watts, and by the time I turned it off at 9 pm it would be consuming 1800 watts or more. What a strange hair dryer this would be!
Bob NH
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bcorbin said:
And what would be the electrical analog of JERK?
JERK is the third derivative of position, or the first derivative of acceleration. In the metric system it has units of meters/sec^3
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