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英语翻译
把以下文章翻译成英语,公式可略
As an illustration of the magnitude of the fluctuations involved,atmospheric pressure is normally 1.012 x 10 5 N/m 2 at sea level; a barely audible signal might fluctuate as little as 10 5 N/m 2 from this value,and a painfully loud continuous noise only about 10 N/m 2,that is,only 0.01°70 of the atmospheric value.(The unit of newtons per square meter,N/m 2,is sometimes replaced by its equivalent,the pascal,Pa.)
2.1 SIMPLE WAVE NATURE OF SOUND
2.1.1 Introduction to Longitudinal Propagation
Wave motion or vibration is made possible by inertia and elasticity in a material.Because of inertia,matter remains at rest or in uniform motion in the absence of external forces; this permits the transfer of momentum between neighboring particles or elements in a medium.Elasticity designates the tendency of displaced elements to return to their original or equilibrium position after the passage of a disturbance.Air,water,glass,and such metals as steel and iron are relatively elastic.
Wave propagation may be demonstrated by the use of a long helical spring fixed at one end.If a disturbance is imparted at the free end,the motion is carried through the adjacent coils,while at the same time the initially displaced coils tend to return to their former positions.The net effect is to produce two distinct regions that travel down the coil structure:in one,a series of neighboring coils are pushed close together because of the initial action of the disturbance (compression); in the other,the relative spacing of coils is enlarged because of the removal of the disturbing force and subsequent overcompensation by the elastic coils (rarefaction).
The wave nature of sound in air may also be demonstrated by the device presented in figure2.2.
图2.2及其说明
The action of the piston in figure 2.2 alternately pushes the air molecules together or pulls them apart.It is the inherent elasticity of air,combined with inertia,which allows these successive disturbances to travel down the tube as the displaced molecules try to regain their former equilibrium.The net effect on the pressure distribution is maximum pressure amplitude at points of maximum compression and minimum pressure at points of maximum rarefaction.If the disc rotates at a constant speed,then the wave form,as represented by the pressure,will be sinusoidal.Figure 2.3 shows some of the characteristics of this simple wave form,termed a longitudinal plane progressive wave because the elements of the medium are displaced in the direction of propagation and the wave is not stationary in space.Waves that propagate in many duct noise control problems or at large distances in free space from a spherically radiating source closely approximate longitudinal plane progressive waves.
图2.3及其说明
把以下文章翻译成英语,公式可略
As an illustration of the magnitude of the fluctuations involved,atmospheric pressure is normally 1.012 x 10 5 N/m 2 at sea level; a barely audible signal might fluctuate as little as 10 5 N/m 2 from this value,and a painfully loud continuous noise only about 10 N/m 2,that is,only 0.01°70 of the atmospheric value.(The unit of newtons per square meter,N/m 2,is sometimes replaced by its equivalent,the pascal,Pa.)
2.1 SIMPLE WAVE NATURE OF SOUND
2.1.1 Introduction to Longitudinal Propagation
Wave motion or vibration is made possible by inertia and elasticity in a material.Because of inertia,matter remains at rest or in uniform motion in the absence of external forces; this permits the transfer of momentum between neighboring particles or elements in a medium.Elasticity designates the tendency of displaced elements to return to their original or equilibrium position after the passage of a disturbance.Air,water,glass,and such metals as steel and iron are relatively elastic.
Wave propagation may be demonstrated by the use of a long helical spring fixed at one end.If a disturbance is imparted at the free end,the motion is carried through the adjacent coils,while at the same time the initially displaced coils tend to return to their former positions.The net effect is to produce two distinct regions that travel down the coil structure:in one,a series of neighboring coils are pushed close together because of the initial action of the disturbance (compression); in the other,the relative spacing of coils is enlarged because of the removal of the disturbing force and subsequent overcompensation by the elastic coils (rarefaction).
The wave nature of sound in air may also be demonstrated by the device presented in figure2.2.
图2.2及其说明
The action of the piston in figure 2.2 alternately pushes the air molecules together or pulls them apart.It is the inherent elasticity of air,combined with inertia,which allows these successive disturbances to travel down the tube as the displaced molecules try to regain their former equilibrium.The net effect on the pressure distribution is maximum pressure amplitude at points of maximum compression and minimum pressure at points of maximum rarefaction.If the disc rotates at a constant speed,then the wave form,as represented by the pressure,will be sinusoidal.Figure 2.3 shows some of the characteristics of this simple wave form,termed a longitudinal plane progressive wave because the elements of the medium are displaced in the direction of propagation and the wave is not stationary in space.Waves that propagate in many duct noise control problems or at large distances in free space from a spherically radiating source closely approximate longitudinal plane progressive waves.
图2.3及其说明
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