In class 11 Physics chapter 13, a brief overview of SHM is given. Simple Harmonic Motion or SHM is periodic motion in which an object repeatedly moves back and forth through an equilibrium or center position. In this way the maximum displacement of one side is equal to the maximum displacement of the other side. In this type of motion, the acceleration and resultant force of the system are proportional to the displacement and act in the opposite direction of the displacement. A pendulum swinging back and forth (from a middle position) is an example of simple harmonic motion.