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In a compressible sound transmission medium - mainly air - air particles get an accelerated motion: the particle acceleration or sound acceleration with the symbol a in metre/second². In acoustics or physics, acceleration (symbol: ''a'') is defined as the rate of change (or time derivative) of velocity. It is thus a vector quantity with dimension length/time². In SI units, this is m/s². To accelerate an object (air particle) is to change its velocity over a period. Acceleration is defined technically as "the rate of change of velocity of an object with respect to time" and is given by the equation : where *''a'' is the acceleration vector *''v'' is the velocity vector expressed in m/s *''t'' is time expressed in seconds. This equation gives ''a'' the units of m/(s·s), or m/s² (read as "metres per second per second", or "metres per second squared"). An alternative equation is: : where : is the initial velocity (m/s) is the final velocity (m/s) is the time interval (s) Transverse acceleration (perpendicular to velocity) causes change in direction. If it is constant in magnitude and changing in direction with the velocity, we get a circular motion. For this centripetal acceleration we have : One common unit of acceleration is ''g-force'', one ''g'' being the acceleration caused by the gravity of Earth. In classical mechanics, acceleration is related to force and mass (assumed to be constant) by way of Newton's second law: : == Equations in terms of other measurements == The Particle acceleration of the air particles ''a'' in m/s² of a plain sound wave is: : 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「particle acceleration」の詳細全文を読む スポンサード リンク
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