We can define quantum mechanics as:

“Quantum mechanics is the theory which describes motion of things at microscopic level.”

In Physics we deal with 3 types of mechanics these are:

1.Classical mechanics

2.Statistical mechanics

3.Quantum mechanics

1.Classical mechanics:

It deals with the physical laws of nature that account for the normal world but break down at very small size (say quantum world ) or at very Large speed and heavy object (say relativity). The flagship equation of classical mechanics is Newton’s second law of motion:

F=dp/dt

2.Statistical mechanics:

It deals with statistical laws to make theoretical predictions about microscopic systems of Particles. Let’s consider an example of a box now if we want to study its motion we have to study velocities, momentum and other properties of all the Particles with which the box is made up of. Consider a box made up of 10^300 particles so in order to study it’s motion we have to study velocities and momentum of all these particles we know that doing this is practically impossible because a box is composed of million of Particles so statistical mechanics deals with averages and approximations. The flagship equation of statistical mechanics is Boltzmann’s entropy formula:

S=k log w

S is entropy, k is Boltzmann constant and w is no. of microstates present in system.

The specific detailed microscopic configuration of a system is called microstate.

3.Quantum mechanics:

Quantum mechanics is completely different from other types of mechanics. If classical Physics describes the world to be deterministic where entire future course is predefined. The Quantum mechanics is based on the assumption that world is probabilistic and events take place at random chances. The most important quantity which we deal with in quantum mechanics is wave function or state of function. The flagship equation of quantum mechanics is schrödinger’s wave equation or we can also use Paul Dirac’s equation which is relativistic unlike schödinger’s equation.