It’s going to have some metadata to that effect yes, like a file index or number of parts or total extracted file size. I don’t know the details, I’ve used them I haven’t read the spec. rar is Rarlab’s proprietary format so there might not even be a public spec.
They’re normally all the same size except for the last part, so it’s not that file 1 is just an index.

Yes, it asks for the next part if it’s not in the same folder with the same name, doesn’t really make a difference what it’s stored on. Multipart zip and tar also exist.

Multipart archives still exist. They’re now used for file sharing websites that have a maximum file size. Before that they were for unreliable p2p networks, so you didn’t lose the parts you’d already downloaded when your peer goes offline. Originally it was to fit something big on multiple cd-roms or floppies.

Opening somthing.rar also reads the data in somthing.r01 through somthing.r15 etc

Yes, suspended weights, also spinning flywheels, hot salt, hot sand
There’s options besides pumped hydro, hydrogen and batteries

Perhaps I should read Ursula’s bag theory myself, because I’m not quite following how it applies to Solarpunk or talking about climate from this.

I like everything I’ve read of Le Guin. Just finished reading her last one, Lavinia (Pre-Roman historical myth based on the Aeneid). The Dispossessed is great and you get a feel for an anarchist society. She also wrote a good translation of the Tao te Ching.

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I also think of public libraries when I hear library; but technically yes. There are libraries where you can go read the material but not lend it out.