Uh, change of topic: isn't the caloric value of a food how much heat can be released by burning it (probably when it is dehydrated)? Plenty of energy stored in a sandwich, sure. But a car battery could power a small spaceheater-like thing for... a while. There's a lot of potential for heat production in a car battery (even without BURNING it). Did Mr. Munroe get this one wrong?
> The efficiency of human muscle has been measured (in the context of rowing and cycling) at 18% to 26%. The efficiency is defined as the ratio of mechanical work output to the total metabolic cost, as can be calculated from oxygen consumption.
The kinetic potential battery (the weight lifted against gravity) is also very efficient.
Food is very energy dense. https://what-if.xkcd.com/128/ (sandwich vs battery)
Uh, change of topic: isn't the caloric value of a food how much heat can be released by burning it (probably when it is dehydrated)? Plenty of energy stored in a sandwich, sure. But a car battery could power a small spaceheater-like thing for... a while. There's a lot of potential for heat production in a car battery (even without BURNING it). Did Mr. Munroe get this one wrong?