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A wave is not transported by a medium in which the wavelength is small compared to the inter-particle spacing of the medium.
The Doppler Effect is the apparent change in frequency of a wave due to the relative motion of the source and the listener.
If the two are approaching one another (due to the motion of either or both), there is a shift to a higher frequency.
If the two are moving away from one another, the listener receives a frequency lower than that produced by the source.
The intensity of a sound is the time rate at which the sound energy flows through a unit area normal to the direction of the propagation.
The intensity of a sound in a uniform medium is inversely proportional to the square of its distance from the point source.
At 1000 Hz, the intensity of the average faintest audible sound (the threshold of hearing) is 10-12 W/m2.
Relative intensity is calculated by this equation: ß = 10 log I / Io
ß is the relative intensity in decibels,I is the intensity of the sound, and Io is the threshold of hearing.
A small source uniformly emits sound energy at a rate of 2.0 W. Calculate the relative intensity at 34 m from the source.
A jet plane is found to have a relative intensity upon takeoff of 110 dB. Calculate the intensity of the sound the jet makes.
The threshold of pain is the upper intensity level for audible sounds. Above this level pain is produced rather than hearing.
When a vibrating object is put in contact with another object, the vibrating object can force the other object to vibrate at the same frequency, increasing amplitude.
All objects that vibrate do so at a certain frequency (or frequencies) called the natural frequency.
This is the frequency where minimum energy is required to cause forced vibrations, and:the least amount of energy is required to continue the vibration.
When the sound produced by one object causes another object to vibrate at its natural frequency it is called resonance, or sympathetic vibrations.
Resonance occurs when the natural vibration rates of of two objects are the same or when the vibration rate of one is equal to one of the harmonics of the other.
Because of resonance soldiers “break step” when crossing bridges.Some bridges have signs that say “No galloping horses” for the same reason.