May 13th, 2009

geek shirt by the falls

More than the integral of r squared dm.

One of the things you discover when you are a physics student, or even a former physics student, is that a great many people will automatically assume that any objections you have to colloquial misuse of physics terms are 1) abstruse and 2) fundamentally stupid. The assumption here is that in catching the technical detail, the physicist (or ex-physicist!) is missing the larger and possibly more poetic analogy.

This is too bad, because sometimes the actual meaning of the word would be really useful if only we could get at it. No, this is not a rant about "quantum." Alas.* The word I want this time is "inertia."

See, I keep hearing people talking about having a lot of inertia as though it means that a body at rest tends to stay at rest unless acted upon by an outside force, full stop. But it also means that a body in motion tends to stay in motion unless acted upon by an outside force. Inertia is not just sitting there like a lump, it's barreling down the tracks full speed ahead. It's a tendency to keep on with what you were doing before, and what you were doing before isn't always nothing.

So when I say I'm having trouble with inertia, it's not getting started that's the problem. It's starting and stopping and changing directions and going in circles. It's the whole thing. And really mostly not the body at rest part. If we were better at the body at rest part, the other stuff might be easier. But not all of it, because sometimes I really don't like the vectors of change here.

*Short version of the rant: "quantum" does not mean "really big." Go ahead and say, "great leap" or "huge leap" or "ginormous leap" when this is what you mean; "ginormous" will make you sound less clueless than misusing quantum here. Mini-rant over; we now return you to your main ramble.