Waves which are involved in many aspects of life, are disturbances that propagate through a medium with a definite speed. A wave of light conveys information to the eyes, a wave of sound brings music to the ears, a water wave rolling onto a beach can topple the swimmer, and electromagnetic waves cook food (microwave oven), and carry television reception. It takes energy to create the wave disturbance, and how the wave travels through the medium (elastic or damped) is quite variable.

There are two important categories of waves, mechanical and electromagnetic. Mechanical waves require a material medium. Water waves in a pond require water, sound waves in a room require air, a stadium "wave" must have people, and a wave produced by plucking a guitar string needs a string. Mechanical waves are produced when the medium is disturbed. A stone dropped in a pond disturbs the water...