# How did the concept of energy evolve with the years?

The concept of energy is quite common today but this was not the case before. As far as I know, even Newton, for example, didn't use this concept and Liebnitz just noticed that $mv^2$ was conserved without a deeper understanding of this.

The concept itself evolved with the years. At this moment my understanding is that: first there was an understanding of work which lead to an understanding of kinetic and potential energy and, hence, mechanical energy.

Then with thermodynamics this was better understood with the addition of heat as a way of transfering energy and, with relativity, also rest energy appeared.

Now, this is probably inaccurate and it's just the impression I got based on what I studied up to now. I would like to know with more details how the concept of energy evolved with time. Where was it born and how along the history of Physics did it become what we use today?

This question might seem "too broad", but just listing the main points in history that contributed to this evolution of the energy concept and some references to see the full history is already a good way to answer it.

• Albeit not an off-topic but best suited here. – user36790 Apr 7 '15 at 3:43
• If the community thinks it is off topic for us, we can migrate to History of Science and Mathematics. Note the relevant meta question. – David Z Apr 7 '15 at 4:40
• I think it is off topic, looks like a history question to me... – hft Apr 7 '15 at 5:54
• @user36790 I agree. It shouldn't be off topic here, but it is liklier to get a good answer at History of Science and Mathematics SE. There are probably more real historians there, even though many straight physicists also get a good feel for history. – Selene Routley Apr 7 '15 at 7:38
• Possible duplicates: physics.stackexchange.com/q/67955/2451 , physics.stackexchange.com/q/132754/2451 and links therein. – Qmechanic Apr 7 '15 at 9:58

You can find here a brief summary of how the concept evolved.

You should not be misled by the different terms, because you are more familiar with the current terms, and with the subtle differences between them: down to Newton's time the language of science and physics (just a branch of philosophy; Naturalis Philosophia) was Latin, a dead language with inadequate lexicon.

The word motus was indifferently used for energy, speed and momentum and the word vis was used for 'force'.

After the philosopher mentioned in the link, it was Galileo that picked up the word 'impeto', but this time the concept is not so vague anymore and corresponds to 'kinetic energy'. The difference was at last made clear by Leibniz, who unmistakably (and not without a deeper understanding) distinguished between vis viva, i.e.:'[kinetic] energy' and vis mortua, i.e.: 'momentum'.

This term was referred to motion, and only later (with thermodynamics) the term 'energy' was extended to other forms of energy, and the qualifier 'kinetic' was appended to identify the original vis viva

If you want further details you may google for 'Leibniz Descartes'/'Leibniz Newton'/ 'vis viva' controversy.

I'd like to add two points to describe the history after the events and people described in Svetlana'a answer:

1. After James Joule discovered the relationship between mechanical work and the generation of heat in about 1850, in the hands of the nineteenth century thermodynamicists (Clausius, Gibbs and especially Thomson (Lord Kelvin)) the notion of a budget and conservation took firm shape: a system seemed to contain a "budget" - a capacity for work- and you could choose what to spend that "budget" on, but, as long as you tallied up the expenditure correctly (as chemical, contribution to potential energy of a field, and so forth) the available budget was always the same.

2. Nowadays we understand conservation of energy as the conserved Noether charge that corresponds to the invariance of the Lagrangian form of physical laws with respect to shifts in the origin of the time co-ordinate. This notion dates from 1918 and was the legacy of Amalie Emmy Noether.

See the Noether's Theorem Wikipedia Page for more details on point 2. The Energy Wikipedia page also summarizes the history of the notion pretty well.

• +1: A very intuitive answer especially for mentioning Noether's theorem. – user36790 Apr 7 '15 at 8:46