alt Hacker NewsEnergy is conserved in Galilean relativity. The thing you're trying to say is that it's not invariant across reference frames.
The answer linked above actually takes advantage of the fact that energy is not the same in different reference frames in order to make the argument work.
I think you are overthinking the heat thing. If you have a train car full of hot water and you slow the train down (extracting kinetic energy from it) until it stops, the water in the train car does not change temperature at all, other than a bit of sloshing around and loss of heat to the surroundings.
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thinking aloud here - so it seems like 2 things are taken as intuitive here:
a) energy is conserved in any frame of reference. b) energy can vary in 2 frame of references.
but then what it feels like is that when you reference the energy as mE(v), the v is actually not the only variable, and it will be more like mE(v, v_moving_reference)?
so we also must take intuitive that c) E(v, v_moving_reference) == E(v - v_moving_reference)
Yes that is what I meant. It’s not the same across reference frames.
I don’t find the OP a convincing argument. What is temperature, why can you assume it didn’t change and the measurement also didn’t change commensurately? Why should kinetic energy be convertible with thermal energy? Chemical energy?
It’s very hand wavy and introduces many assumptions.
Kinetic energy is a book keeping trick. The real mystery is explaining how it relates to other forms of energy and how to tie it together.