[Bored chemist]

No, it is principle. You can cry or shout louder, it remain... a principle.
Sorry to talk science.

Here is the proof.
https://en.wikipedia.org/wiki/Noether%27s_theorem

Why do you do this?

[Deecart]

Here is the proof.

It is not a proof fo me, it is just a link
What is your argument ?

[Deecart]

Why do you do this?

Try to do say something that someone can understand.

[Kryptid]

Here is the proof.

It is not a proof fo me

Not understanding a proof doesn't mean it isn't proof. Do you know what a theorem is?

[Bored chemist]

Why do you do this?

Try to do say something that someone can understand.

Why do you insist on saying things like "it has not been proved" even though (1) it has been and (2) you do not know anything about the subject?

[Bored chemist]

It is not a proof fo me, it is just a link

It is a link to the proof that mass/ energy is conserved.
Would it really help if I copied and pasted the proof into this thread?

[alancalverd]

No, it would (and was, because before we understand that coal was cointaining energy, every vapor machine was a over unity machine) be some machine that "produce" energy from an actually unknown energy source.

This raises an interesting point. It is doubtful whether anyone considered the idea of a conserved "quantity of work" as being useful before Leibniz, nor whether it became a "popular" feature of physics before Newton. It had always been obvious that you need to put something (food or fuel) into a device (horse or furnace) to get it to do useful work, but the need for numerical analysis really arose when Newcomen began manufacturing steam engines commercially in the 1700s, at which point purchasers wanted to know how much coal was required to pump a given quantity of water from a mine.

This produced a quaint British idiom "nineteen to the dozen", now used to mean "at a great rate" but originally an advertised measure of efficiency:

When going nineteen to the dozen something or someone is going at breakneck speed. The origin here is one of the nicest that I have come across. It goes back to the time of the Cornish tin and copper mines. These mines were often hit by floods. In the 18th century coal powered, steam driven pumps were installed to clear the water. When working maximally the pumps could clear nineteen thousand gallons of water for every twelve bushels of coal.

Arguably the earliest description of energy efficiency, though the lift height isn't specified in most accounts.