The document discusses simple harmonic motion (SHM). It defines SHM as motion where the acceleration of a particle is directly proportional to its displacement and always directed towards the mean position. Linear SHM is given as an example where the displacement follows a straight line path, such as the motion of a spring-mounted mass. The differential equation of SHM is derived as ∂2x/∂t2 = -ω2x, where ω is the angular frequency. Key characteristics of SHM including amplitude, period, frequency, and phase are also defined. Examples are provided for linear and angular SHM motions.