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Sunday, April 15, 2012

What's a Watt?

A Watt is a unit of energy flow or power named after James Watt, the steam engine guy. There are lots of energy terms. According to Wikipedia, a Watt is defined as a Joule/second which is a measure of energy conversion or transfer. Since it is a flow thingy, you have to know the area it is flowing through and how long it is flowing. The units for the power then is in Watts per meter squared per some period of time. Since it is defined as a Joule per second, there are 60 seconds in a minute and 60 minutes in an hour, there are 3600 Joule/seconds in a Watt hour. A kilowatt hour would be 3,600,000 Joule seconds.

So should I say that there is only 0.1 Joules/second-meter squared of energy flow, that would be tiny. If that flow was through the surface of the Earth with an area of 510,000,000 kilometers squared which is 510,000,000,000,000 meters squared, it would still be small to most folks thinking. At 0.1 Wm-2, that would be 5.1 x 10^13 Joules per second or Watt-seconds. Since there are 3.6 x 10^6 Joules per kilowatt-hour, that would only be 1.42 x 10^7 Kilowatts per hour. That is about 14.2 GigaWatts per hour. Big number, but still small to most folks.

In order for those folks to consider it significant, it takes more time, say 40 years. There are 60x60x24x365.25x40 equals 1.26 x 10^9 seconds in 40 years. I have lived more that that many seconds, so from experience I can tell you that is not a very long time. Now with 1.26 x 10^9 seconds and 5.1 x 10^13 Joules per second you end up with 6.44 x 10^22 Joules. That seems like a lot of Joules. Still that is not much to some folks. Those folks think that 22 x 10^22 is a lot of Joules. Well it is a little over three times as much as the not so much 6.44 x 10^22 Joules. If you convert it to kilowatt hours, the number is even smaller. It is only like running a 14.2 gigawatt-hour power plant 24/7/365 for 40 years. Nothing right?

If the surface of the Earth was to cool from 288K to 287.8K, that is not much either. That would only be 1Wm-2 less energy radiating from the surface if the surface were a true black body. That is ten times as much as 0.1Wm-2, so that would be like running the 14.2 gigawatt-hour power plant for only four years, 24/7/365.

Well, the average surfacetemperature of the World's oceans is more than 288K degrees. They are closer to 294.25 K degrees. If their temperature dropped to 294.225, a 0.025 K degree drop, that would be like 0.1Wm-2 less energy, which must also be insignificant to most.

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