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Where When How N/D 2017 - J/F 2018 : Page 89

–Silent World ] the Sea sound Off — The Basics Before delving into the nuances of sound underwater, the more basic question is, just what is sound? Sound is a form of energy transmitted by rapid pressure changes in whatever it moves through. The substance that sound travels through is called a medium, which can be anything — liquid, solid or a gas — but must be something. So, contrary to what you see in “Star Wars” or “Battlestar Galactica,” sound cannot travel in space because space is a vacuum; there is no medium through which sound can travel. So how does sound travel in this medium? As we’re inter-ested mainly in how sound behaves in water, imagine tiny parcels of water as individual particles. When sound transits By Alex Brylske the water, the particles receive a minimal push, then a pull, causing them to vibrate back and forth. The spot where a par-ticle was before the sound wave came through is called its equilibrium position. The movement of the water particle is called vibration. A sound wave is called a compressional or longitudinal wave. The particles in a longitudinal wave move parallel to the direction in which the wave is traveling. This is illustrated in Figure 1. Note that there are places where the particles are squashed together (compressed) and places where the parti-cles are pulled apart (expanded). The compressed areas rep-resent regions of high pressure, while the expanded areas are regions of low pressure. So, a sound wave alternately com-presses and expands whatever medium it travels through. Photos and charts provided by Dive Training Visit the Turks & Caicos Islands at www.WhereWhenHow.com NOV/DEC/JAN/FEB 2017/2018 • • • • • 89

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