4 ms·

> given how off your tidal plant calculation is I wouldn't be surprised if it's way off as well. he showed his work for his first calculation. Looked reasonab

• avar 9y ago
  His numbers look fine, but I think the assumptions are false. > And these furnaces are maybe 50 feet across. [...] > So the Earth has a heat stored which is > (4K miles / 50 feet)^3 This seems to assume that the earth is also cube shaped like a hypothetical 50ft^3 blast furnace, instead of a sphere (or oblate spheroid before anyone out-pedants me). It also seems to assume that a 50ft^3 blast furnace contains energy equivalent to 50ft^3 of molten mantle. If you look at diagrams of blast furnaces you can see that a relatively tiny part of them is actually molten material. Not being able to find numbers on the stored joules of industrial blast furnaces, I'm just going to just state that 50ft^3 of mantle has a crapload more potential energy than 50ft^3 of blast furnace, most of which is air, equipment & empty space, not molten material. He is right that there's at least as much energy stored in the earth as he's saying, but it's going to be a crapload more than that. The insides of blast furnaces are also significantly colder than the average temperature of the mantle.
  • adekok 9y ago
    The point is that these are "back of the envelope" calculations. Fermi was known for asking questions like "how many gold balls git into a suitcase". The point isn't to get a perfect answer. The point is to get a reasonable answer. In this case, the point is to answer the OP question in laymans terms. Using not much more than reasonable assumptions, and grade 5 math. Or, you can bike shed over details.