What is Sound?

Sound: is a wave that is created by vibrating objects and propagated through a medium from one location to another.  It is a longitudinal wave.

Sound waves are similar except that they are much higher frequency and it is air that is being alternately compressed and expanded rather than the coils of a spring.

​How Sound Travels.

First, there is a medium that carries the disturbance from one location to another. 

Second, there is an original source of the wave, some vibrating object capable of disturbing the first particle of the medium. 

Third, the sound wave is transported from one location to another by means of particle-to-particle interaction.

​Pitch

Pitch: perceived frequency of sound. High pitch is high frequency and low pitch is low frequency.

The lowest frequency humans can ordinarily hear is a deep hum at a frequency around 20 Hz.

Even this frequency is so fast that you cannot see the vibration with your eye; instead, you can only see a slight blur.

Loudness

The loudness of a sound depends on the amplitude of the wave. A loud sound has a larger amplitude than a soft sound of the same frequency. 

The loudness of a sound relates the intensity of any given sound to the intensity at the threshold of hearing.
It is measured in decibels (dB). The threshold of human hearing has an intensity of about .0000000000001 watts per meter squared and corresponds to 0 decibels. 

Intensity

Sound Intensity is defined as the sound power per unit area in a direction that is perpendicular to that area.

Intensity=Energy/(time x area) =  Power/Area

The distance vs. intensity is an example of the inverse square law

​Speed of Sound and Temperature

The speed of sound is affected by temperature in a given medium. For air at sea level, the speed of sound is given by

v_w=(v)√T÷273K,

where the temperature (denoted as T) is in units of kelvin.
The speed of sound in gases is related to the average speed of particles in the gas, v_rms and that:

v_rms=√3kT÷m.
k = 1.38 x 10^-23J/K
m = mass of the particles

Doppler Effect

Doppler Effect: shift in frequency of a wave that is emitted from a source that is moving with respect to the observer.

There is an apparent upward shift in frequency for the observer and the source are approaching and an apparent downward shift in frequency when the observer and the source is receding. 

f= f_o(v_s/(v_s-v))