Quantum mechanics is a theory describing movements at the microscopic level. It is one of three main types of mechanics, alongside classical and statistical mechanics. Classical mechanics focuses on the motion of the center of mass of an object, represented by Newton's second law of motion. Statistical mechanics delves into studying the motion of every particle within an object, but due to the immense number of particles involved, averages and approximations are used. It is applied when dealing with ensembles of atoms or molecules.