Characteristics of Wave Motion

Three general characteristics hold for wave motion of any kind. First, for a wave to propagate through a medium at all, that medium must possess both inertia (mass, giving it something to accelerate and decelerate as the disturbance passes) and elasticity (a restoring force that pulls displaced particles back toward equilibrium); together, these two properties determine exactly how fast a wave can travel through that particular medium. Second, within any one given medium the wave's own overall velocity stays constant, even though the individual constituent particles of the medium are themselves moving with continuously changing velocities at different positions along the wave -- a particle's own oscillation speed is maximum as it passes through its mean (equilibrium) position and drops to zero at the extreme points of its displacement, exactly like a mass in simple harmonic motion; this particle velocity must never be confused with the wave's own steady propagation velocity. Third, waves in general -- not just sound or light specifically -- are subject to the same broad family of phenomena: reflection (bouncing off a boundary), refraction (bending when passing betwe …