Sir Isaac newton is the undisputed father of classical physics.

Classical physics is the physics without considering quantum mechanics. This is the type of physics practiced by for example Newton (you might also come across the term Newtonian physics). General relativity is also a classical theory.

The distinction is often used because quantum mechanics changed quite a bit in many fields of physics, so the term 'classical physics' allows for a clear distinction.

The opposite of classical physics would be quantum physics.

impossible & inexplicable. in classical physics radioactivity simply can't happen.

actually, classical physics can be formulated as an approximation of the laws of quantum theory, where the Planck constant tends to 0.

classical physics and (Quantum or modern) Physics