give breif about classical mechanics,quantum mechanics,relativistic mechanical,quantum field theory

Kindly post your questions in different threads to get all the answers.
Refer to the links given below to know about  classical mechanics and quantum mechanics
https://www.meritnation.com/ask-answer/question/what-is-classical-machanics/physical-world/5206324

https://www.meritnation.com/ask-answer/question/what-is-quantum-mechanics-explain-its-principles-and/structure-of-the-atom/3478643