In all our activities, the availability of energy is a continuous problem. The conversion of energy into a useful form and the transportation of this energy from the point of conversion to the point of use are matters of immediate concern. In different communication procedures the message is carried through the motion of waves or through the motion of matter (particles). Waves enable the transfer of energy from one point to another without the physical transfer of matter between the points. Sounds reach our ears by means of air waves. Radio signals are waves that transmit music or speech. All waves have certain properties in common that will now be discussed.