What+is+sound?

What is sound? It's all around us. We produce it, we take it in, we observe it without even thinking about it consciously.

Sound is measured in various ways, using various techniques and units. One of the most popular units used for measuring sound is hertz. Hertz is a measure of the sound frequency. The number of cycles per second of a sound wave is its frequency, which is measured in this unit, hertz. Another way to measure sound is in decibels. To give you an idea of the decibel level of things you come in contact with on a daily basis, refer to the chart below. A sound over 120 decibels will do serious damage to the human ear and will be very painful to listen to. Anything over 85 decibels can cause slight damage or serious damage if built up over time. The photo below shows a decibel meter reading of a person singing. Here is a chart showing different decibel readings: Source: http://www.ndt-ed.org/EducationResources/HighSchool/Sound/components.htm Sound travels in waves. A sound wave is a **mechanical wave**. This means that sound moves through a medium from one particle to the other. A medium is something that sound moves through. For example, when you think of sound, you think of it moving through air. Air is the medium. Another example of a medium is water. The movie below shows a Chladni plate, which is a convenient way to demonstrate the movement of sound through waves. When a frequency coming out of a speaker causes the Chladni plate to vibrate, it vibrates in a pattern according to the certain frequency and that pattern changes when frequency or amplitude changes. Sand is poured onto the plate to show the actual pattern of vibration, complete with nodes (the point of no vibration). media type="file" key="Movie 10.mov" width="300" height="300" media type="file" key="Movie 14.mov" width="300" height="300"