Pardon me for taking something too seriously:
A lot of my friends are passing around this article from The Onion. It is really funny, as usual, but there’s an annoying error in it. Yes, I know the whole article is intended as a joke, but not every untrue thing is funny. I’m talking about a mistake with units of measurement, which is pretty much like a grammatical error, except that it actually matters, as I’ll explain below. The article is about congress approving a monument which is a tribute to human folly. Its got a big energy-wasting light at the top, and to make it sound like its really wasting a huge amount of energy, they wrote that it will “use a staggering 12 gigawatts of power per second.” I’m not saying the number it too big: Nuclear power plants produce about a gigawatt of power, so yeah, the number 12 is on the funny side of big. What I’m saying is that a “gigawatt per second” isn’t what they wanted.
Power is the rate of energy usage, or transferral or whatever. A 60-watt rated lightbulb consumes about 60-watts of power. You could also say that the same bulb consumes about 60 Joules of energy per second, but a watt per second would describe something weird like the rate that the bulb’s energy consumption would change over time. The rate of the rate of energy use. Thats wrong in this context, but not funny-wrong.
Why am I so annoyed by this? Well, when I was learning physics in school, I realized that if I kept the units of a quantity right, I could solve lots of problems without ever memorizing equations. Its not just a trick or a mnemonic. It basically gives structure to how one thinks about a problem, and its pretty powerful. This type of thing is called dimensional analysis, and real physicists use it to guide them in research. I have an awful memory, and can’t memorize equations or anything, but dimensional analysis basically got me through the Subject GRE and the Qualifier Exams. If you want to learn physics, or if you just want something to help you when think about any kind of quantitative stuff, dimensional analysis is a big help.
Power describes a change in energy per change in time. There. I’m done. Go read the article. Its funny.
PS: Thanks to my friend Tim for pointing this out.
