Sound Waves

 Sound is a longitudinal wave, meaning that the motion of particles is along the direction of propagation.  sound waves are divided into three categories that cover different frequincy ranges: Within the range of sensitivity of human ear. They can generated in Varity of ways. Such as human voice Within the range of sensitivity of human ear. They can generated in Varity of ways. Such as human voice Have frequencies below the audible range. Elephants can use this waves to communicate with one another. Have frequencies below the audible range. Elephants can use this waves to communicate with one another. Have frequencies above the audible range. Dogs hear this waves humans cannot detect it Have frequencies above the audible range. Dogs hear this waves humans cannot detect it

Sound waves- longitudinal waves; compressions and rarefactions that travel through a medium

a point source emitting sound waves equally in all directions. If the air around the source is perfectly uniform, the sound power radiated in all directions is the same, and the speed of sound in all directions is the same. The result in this situation is called a spherical wave. Each arc represents a surface over which the phase of the wave is constant. We call such a surface of constant phase a wave front. The radial distance between adjacent wave fronts that have the same phase is the wavelength l of the wave. The radial lines pointing outward from the source, representing the direction of propagation of the waves, are called rays.

The intensity I of sound wave at a surface The intensity I of sound wave at a surface is The average rate per unit area at which energy transferred by the wave through or onto the surface. P is the time rate of energy transfer of a sound waves inverse-square law The intensity decreases as the square of the distance from the source. This inverse-square law

sound level β (Greek letter beta) is defined by the equation The constant I 0 is the reference intensity, taken to be at the threshold of hearing (I = 1x W/m 2 ), and I is the intensity in watts per square meter to which the sound level b corresponds, where b is measured2 in decibels (dB).

As a wave source approaches, an observer encounters waves with a higher frequency. As the wave source moves away, an observer encounters waves with a lower frequency. This apparent change in frequency due to the motion of the source (or receiver) is called the Doppler effect.

OS If Observer O and the Source S stationary the source emits sound Wave with λ,υ,f First: O is moving and S is stationary

OS If Observer O and the Source S stationary the source emits sound Wave with λ,υ,f Second : O is stationary and S is moving S

SS

Sound source moving toward observer sourceobserverat rest Frequency f s Frequency f o Observer hears increased pitch (shorter wave length)

Resting sound source source at rest observer at rest Frequency f Frequency f o V=340m/s

Sound source moving away from observer source observer at rest Frequency f s Frequency f o Observer hears decreased pitch (longer wave length)

First : S moving with velocity v s = v Sound barrier

Second : S moving with velocity v s > v