Solar Sails and Squirrels

Over at the XKCD blag, Randall discusses solar sails and levitating squirrels. And he’s absolutely right — the Back-to-the-Futuresque 1.21 Gigawatts will levitate about a kg, assuming perfect reflection. Assuming absorption, you vaporize the squirrel in a couple of milliseconds.

(1 kg of water requires about 2.5 million Joules to boil away, starting at body temperature. Or not — the latent heat of vaporization is the dominant term)

I think the XKCD cartoons are often quite funny, BTW. A link, if by some odd chance you were unaware of them. I just got a new light box to replace my broken one. Must find time to draw cartoons.

Let's Geek It UP!

Mar 14th is “Talk like a physicist day,” and there’s a blog dedicated to it. Of course, I’ll be doing so anyway, because that’s what I do. My suggestion is to get familiar with some jargon, and substitute it for smaller words whenever and wherever possible. That’s what we do.

technojargon

(Of course Mar 14th is also Einstein’s birthday and “Pi day” in the US)

Via Cocktail Party Physics

The Geometry of a Cow

There’s an old physics joke about the dairy (Motto: “Smell Our Dairy Air!”) that hires cosultant after consultant to help optimize their milk production but to no avail. Each and every time, the end result is that nothing has improved. Finally they hire a physicist, who comes in and takes all sorts of data, and then retires to his office, madly doing calculations. After waiting a while, the dairy contacts him, inquiring about his recommendations. He come in to do a presentation, with all sorts of papers and slides for the overhead (or powerpoint on his laptop if you want to update the joke). He puts up the first slide, and starts in with, “First, we assume a spherical cow…”

It’s funny if you know physics, or more specifically, physicists, who tend to idealize all sorts of things in their models. (frictionless surfaces, elephants whose mass a may be ignored, etc.)

Anyway, hop in the wayback machine to a few years ago, when several of us were having a discussion about problems on our comprehensive exams in grad school. My boss tells one about a cow on a tether attached to a point on the rim of a cylindrical silo of a given height and radius. You were supposed to calculate the grazing area available to the cow. I, being in a smartass mood (sarcasm is my ground state), ask, “Did you assume a spherical cow?” The didn’t-miss-a-beat response was, “No, I was able to use the point-cow approximation for this problem.” And I thought that was pretty funny, and something that works in a single-panel cartoon.

point_cow.jpg