how did physics evolved?

Answer 1

Like anything evolves - by mutation and natural selection, but within the field of ideas instead of genes. Google memetics. Within the community of folks whose primary interests are to make useful things and predict the outcome of physical processes, physical theories which perform better in this capacity become more widely studied and developed.

Answer 2

I am not sure what you mean: how *has* physics evolved. Historically? This is very interesting.

At the beginning the science was not separated into branches and was called philosophy. It started with count of days and years, geometric measurements, observation of stars (future astronomy).

In the middle ages, the laws of mechanics got understood first; then theory of heat, thermodynamics, electricity + magnetism, then, in the beginning of the 20th century, relativity and quantum theory.

Answer 3

You start with a basic idea - like gravity or electromagnetism - and base a whole field off of it that people are still investigating today.