NPS Physics - Ph 3451: Acoustics - Lecture 1 - Introduction | fluid description | equation of state [video]
Naval Postgraduate School Physics
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A fluid is a gas or a liquid. Compression-expansion waves in a fluid are called acoustic waves. These waves involve the propagation of changes in density, pressure, and temperature. Acoustic waves also occur in solids and plasmas, but these substances are more complicated because a variety of other types of waves can also exist (for example, shear waves). This entire course will deal with linear acoustics, which involves small deviations of the density. The study of finite-amplitude deviations is called nonlinear acoustics. Many new and more-complicated phenomena occur in nonlinear acoustics, and it is best to understand linear acoustics before studying nonlinear acoustics. The elective course PH4459 (nonlinear oscillations and waves) is taught every spring quarter and is open to all students who have had introductory physics and differential equations. This course includes nonlinear acoustics as well as other nonlinear oscillatory systems. Acoustics is actually a special case of fluid dynamics. Because acoustics is so broad, however, it is usually considered to be a separate subject. Some of the different fields of acoustics are: physical (fundamental) acoustics, underwater acoustics, architectural acoustics, musical acoustics, structural acoustics, acoustic transducers, physiological and psychological acoustics, animal acoustics, and insect acoustics. A new field, which can be called environmental acoustics, is rapidly becoming important due to importance of detrimental sound. (This field was previously called acoustic noise). Acousticians are everywhere, and there will always be a need for them! FLUID DESCRIPTION A proper understanding of acoustics begins with fluid dynamics. We consider a fluid particle that has a fixed amount of mass. A fluid particle is small compared to the length scale of changes in the fluid but contains very many molecules.
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