ABSTRACT
This chapter discusses some theoretical aspects of classical mechanics, such as the definition of vectors and tensors. It shows how they get generalised in special relativity. The chapter highlights the genuine novel features of general relativity, making it possible to understand common features of the three theories and how they realise a sort of set of Chinese boxes. Classical mechanics is based on the assumption that physical systems can be described within the Galilean space-time. After achieving a covariant formulation of classical mechanics and electromagnetism, Einstein turned to the investigation of a covariant formulation that would also include gravity, providing a relativistic generalisation of Issac Newton's law. The postulates of special relativity almost coincide with those of classical physics. The chapter discusses according to the Galilean principle of relativity, the laws of classical mechanics are invariant under a Galilean boost transformation. It also discusses basic ingredients of general relativity, necessary for a proper comprehension and derivation of A. Friedmann cosmological models.
