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254 comments on Due Diligence: A reader's response to Khosla

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DIYer on August 13, 2006 - 5:20pm Permalink | Subthread | Parent | Comments top
As TOD gets more subscribers, we'll probably see a smaller percentage who've had a tutorial in dimensional analysis. Watt-hours, electron-volts, Joules, BTUs, ... TOD is likely to toss around a few terms with which the average reader will be unfamiliar.

To make matters worse, I just looked up Joule in Wikipedia, and the entry starts with this misinformation: The joule (symbol: J) is the SI unit of energy, or work ... Gack, energy ≠ work!

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Kevembuangga on August 13, 2006 - 5:49pm Permalink | Subthread | Parent | Comments top
the entry starts with this misinformation: The joule (symbol: J) is the SI unit of energy, or work ... Gack, energy ≠ work!

Sorry, you should read closer or rehearse your courses from long ago.
The very first lines are absolutely correct :

The joule is a derived unit defined as the work done or energy required to exert a force of one newton for a distance of one metre, so the same quantity may be referred to as a newton metre or newton-metre with the symbol N·m.

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WebHubbleTelescope on August 13, 2006 - 5:51pm Permalink | Subthread | Parent | Comments top
same units, perhaps different meaning
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canbrit on August 13, 2006 - 6:41pm Permalink | Subthread | Parent | Comments top
Well, I certainly run out of energy when I do a lot of work!!

But seriously...

Units of Work = joules

Units of Energy = joules

Did I miss something during my Physics degree courses? Care to enlighten us?

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DIYer on August 13, 2006 - 8:39pm Permalink | Subthread | Parent | Comments top
Units are the same, but energy is generally defined as 'ability to do work'. However, I can burn X BTU's worth of energy without getting the equivalent in work. The difference is perhaps a subtle one.
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DIYer on August 13, 2006 - 8:44pm Permalink | Subthread | Parent | Comments top
Actually I was a little hasty with the post button, and would have withdrawn that post if I could. When looking at the Wiki article, I had a blonde moment and thought it said something like 'energy, or power'... Nonetheless, there is a distinction between work and energy.
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Engineer-Poet on August 13, 2006 - 6:50pm Permalink | Subthread | Parent | Comments top
The Wikipedia entry is correct, and now maybe you understand why the public has such a bad understanding of energy issues - it goes right down to the essential terms.
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Squalish on August 13, 2006 - 8:03pm Permalink | Subthread | Parent | Comments top
Just changed the line - energy is defined as the potential for a physical system to do work.
The usage on energy is "I use 7 million joules [of energy] a day to heat my home."

The usage on heat is "Theoretically, my car did about 7 million joules of work to get to the top of that mountain, not counting what it blew on heat"

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