Fine Structure

Gravity Wells from XKCD

There are probably few people who read this blog and don't read xkcd, but I'll link to and put my stamp of approval on today's comic: Gravity Wells.

The idea is that it takes a certain amount of energy to escape a (real, physical) well of some depth. There are no awards for halfway, if you don't have the energy to climb all the way out of the well, you're not out and there's nothing keeping you from falling back down to the bottom. Escaping from the gravity of a planet is very much the same, hence the term "well."

My favorite part is the insets where Randall explains that you can escape the gravity well of Deimos, a moon of Mars, with only a bike and a ramp! More insets! More detail! More bike ramps on captured asteroids! ]