What are some math concepts which were originally inspired by physics? There are a number of concepts which were first introduced in the physics literature (usually in an ad-hoc manner) to solve or simplify a particular problem, but later proven rigorously and adopted as general mathematical tools. 
One example is the Dirac delta "function" which was used to simplify integrals, but at the time was perhaps not very well-defined to any mathematica standard. However, it now fits well within the theory of distributions. Perhaps another example is Newton's calculus, inspired by fundamental questions in physics.
Are there any other examples of mathematical concepts being inspired by work in physics?

The notion of $\color{red}{\text{Derivatives}}$ and more generally calculus.


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*The ancient Egyptians and Greeks (in particular Archimedes) used the notions of infinitesimals to study the areas and volumes of objects.

*Indian mathematicians (in particular Aryabhatta) used infinitesimals to study the motion of moon and planets.

*These notions were later extended and formalised by Newton and Leibniz.

