Munroe uses his physics degree, and considerable talent for explaining things, to explore hypothetical questions on just about every science topic possible. His responses are easily accessible and quite witting as he explains what would happen if you suddenly, endlessly started raising in the air; how long people on a submarine could survive in space; and how far a steak would have to fall to be cooked by the time it landed.
Beyond just answering the questions, Munroe is brilliant at explaining why things are that way. For example, I learned that a steak will never be cooked by falling through the atmosphere because it is too easy for air to get around it. I always thought that things warmed up when the went through to atmosphere because friction, this is not the case.
Interesting tidbit: Water is not very compressible.