An engineering question I like to ask people is: What are the ultimate sources of the power we the human race use? (thread)
The challenge is both to understand the second law of thermodynamics ('gravity' is not a source of energy) and to get all of them. The last one is a doozy. See if you can name them all before reading on.
Chemical stores of energy are relatively small and need to be replenished or they get used up quickly, which is in the process of happening. They mostly occur in the form of Carbon which isn't fully oxidized.
The obvious one is solar, which ultimately comes from fusion in the core of the Sun, which is a mix of the P-P chain and the CNO cycle, fusing Hydrogen using Carbon as a catalyst
Next up is nuclear power here on Earth, in the form of isotopes which have remaining potential energy. This powers geothermal from the decay of Uranium, Thorium, and Potassium, and human-caused fission from Uranium and hopefully a lot more in the future Thorium
In the future we might see human made fusion in the form of fusing Hydrogen (both Protium and Deuterium) and there's a bit of extra juice from decay of stable isotopes after a neutron from one of the above reactions hits them and they decay
Technically nuclear also gets a bit of juice from cosmic rays causing transmutation but thats too small to matter much to us humans, although now I wonder if a big enough planet could stay warm off of it
Now we get into the not obvious ones, which are tidal forces, caused by potential kinetic energy on a massive scale. The first of those is the difference between the length of a day and the length of a year.
The second is the difference between the length of a day and the length of a month. These directly cause the tides. Wind is caused by a combination of solar and tidal forces.
How much each contributes is a very interesting question. But we've left something out, something which is normally completely inaccessible but has most definitely been used one amazing way. What is it?
The final source of power is: The difference between the length of an Earth year and the length of a Jupiter year. If you want to get something of any size out of the solar system there's no way to do it except to slingshot off Jupiter \
thereby bringing the two planets a miniscule amount closer together. Thanks Jupiter!
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