When someone talks or calls out to you, you hear the sound of their voice. When someone turns a light on, light immediately floods the room. How do light, sound, and a lot of other things move from their source to you? They’re not matter! The answer is waves. A wave is a rhythmic disturbance that carries energy, not matter, through the particles of a medium, one of many aspects that make up what we call waves. A wave is made up of many parts. One of them is the medium. The medium is the material through which the wave travels. Think of the wave at a sports stadium. The hands in the air represent the wave, and the crowd, which carries the wave from one end of the stadium to another, could be represented by a medium. Most waves need a medium