Why unit analysis matters

"The two most common things in the universe are hydrogen and stupidity."  Every time I start to forget this, something comes along to remind me.  Sometimes forcefully.
I forget what prompted me to write Unit Analysis.  This time, it was a clown who can neither calculate the area of Earth's disc without getting off by a factor of a million (you'd think the ridiculous number would tip him off), nor can he grasp the meaning of "kilowatt-hour".  Indeed, he insists that "kilowatts per month" is what people pay for on their electric bill.  After receiving a free physics tutorial including definitions of basic units, he topped this off with an insult: "... it would seem you would have problems reading your own electricity meter."
Innumeracy is probably a guarantee of incompetence in basic science, but it takes a special combination of arrogance and ignorance to say "It was written for people to understand how many watts are required in unit time to power things in terms which they understand."
He's too wrapped up in himself to realize that the public doesn't understand these things any better than he does, and one of the biggest reasons they don't is that they don't speak the language.  They could learn it by osmosis, except for one thing:  all the clowns out there mangling the language of physics, producing such a cacophony that the voices of knowledge cannot be distinguished.  In short, Mr. Clown is part of the problem.
Well, why does it matter?
It matters because John Q. Public needs to know that a space heater which consumes 1.2 kilowatts is not going to cost 15 cents a month to run because the electric rate is "12.5 cents per kilowatt".  Anyone who does not understand the way time figures into the calculation — and why the electric bill speaks of kilowatt-hours — is almost certain to get it wrong.  The buyer who estimates the usage time as 6 hours per day, then multiplies 180 hours per month times 1.2 kW to get 216 kWh and calculates $27, will get it right.
To get it right, all you need is to know that a kilowatt-hour is a kilowatt times an hour.  If you keep calling it "kilowatts per hour", you're never going to understand that.
Scientists and engineers use precise language and correct units because that's the only way to get the RIGHT answer.  People who use WRONG language or WRONG units can do things like getting an electric bill of fifty dollars when they thought it was going to be fifty cents.
This is not a matter of opinion; there are a few ways of accurately describing how the world works, and innumerable ways of getting it wrong.  You can use English or MKS or CGS units, but any correct calculation is going to come up with the same answer after conversions.
This is one place where what you don't know really can hurt you.
Unit analysis matters.  Treat it that way.

Labels: innumeracy, unit analysis

  ¶ 12/19/2006 12:41:00 AM 9 comments