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All sounds are produced by the vibration of matter. If there is no vibration, there is no sound.
Sonic spectrum - frequency range over which longitudinal waves occur.
A wave is not transported by a medium in which the wavelength is small compared to the inter- particle spacing of the medium.
Sound - range of compression-wave frequencies to which the human ear is sensitive.
This audio spectrum extends from approximately 20 to 20,000 hertz.
Frequencies above the audio range are ultrasonic. Frequencies below are infrasonic.
Sound waves are longitudinal waves. (Compressions and rarefactions.)
To produce sound waves, there must be a source of mechanical disturbance and an elastic medium.
Sound does not travel through a vacuum. (In space no one can hear you scream)
The speed of sound in air at 0° C is 331.5 m/s. This speed increases with temp. about (0.6 m/s)/C°.
Speed of sound in water is about four times that in air. It is even faster in some solids.
Factors that affect sound speed: 1) temperature, 2) density, 3) elasticity.
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.
This apparent shift of frequency is demonstrated by all types of waves, not just by sound.
Three physical properties of sound: intensity, frequency, and harmonic content.
The effects of these on the ear are : loudness, pitch, and quality.
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.
I = P / A P is power in watts. A is area in square meters. I is intensity in watts/ meter 2.
The intensity of a sound in a uniform medium is inversely proportional to the square of its distance from the point source.
Loudness depends on an auditory sensation in the consciousness of a human listener.
At 1000 Hz, the intensity of the average faintest audible sound (the threshold of hearing) is 10 -12 W/m 2.
Relative intensity is calculated by this equation: ß = 10 log I / I o ß is the relative intensity in decibels, I is the intensity of the sound, and I o 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.
These are called forced vibrations.
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.
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