CLIL CLIL CLIL PHYSICS WHAT IS SOUND? Imagine that a stone is thrown into a still body of water. The rings of waves expand indefinitely. The same is true with sound. Regular repeating sound waves create musical notes, while irregular repeating sound waves produce noise. When the vibrations are slow, they create a low note. When the vibrations are fast, you hear a high note. Sound waves are produced by a vibrating body, such as an oboe reed, guitar string, loudspeaker cone or jet engine. The vibrating sound source causes a disturbance to the surrounding air molecules, causing them to bounce off each other with a force proportional to the disturbance. The energy of their interaction creates ripples of more dense (higher pressure) to less dense (lower pressure) air molecules, with pressures above and below the normal atmospheric pressure. When the molecules are pushed closer together, it is called compression; when they are pulled apart, it is called rarefaction. This back and forth oscillation of pressure produces a sound wave. Sound waves in air are longitudinal waves, in that the pulsating motion of the air is in the direction the sound wave travels. 260