Question

what are the differences between simple & physical pendulum?

Answer 1

simple pendulum
A hypothetical pendulum suspended by a weightless frictionless thread of constant length
physical pendulum
Pendulum consisting of an actual object allowed to rotate freely around a horizontal axis

Answer 2

A simple pendulum is a point mass on the end of a mass less string or rod. This is obviously not possible to have in a realistic scenario, but can be approximated when the length of the string is > than that of the mass.

A physical pendulum is just anything that has mass swinging back and forth like a pendulum, but you can't deal with it the same way it has mass at each of the points up to the center so you have to calculate it's rotational inertia before you can do any meaningful calculations.