Sound is a compressional wave caused by the vibration of an object. Waves can travel as transverse or compressional waves, depending on the relationship between the movement of energy and the movement of the medium; if the medium moves at a right angle to the energy, it is a transverse wave, and if it moves in the same direction as the energy, it is a compressional wave.
Figure 1- a transverse wave and a compressional wave.
Qualities of a sound
Figure 2- a transverse wave, labelled.
Sounds can be differentiated from each other through identifying its qualities, such as pitch, amplitude, speed and timbre. Pitch is able to be determined by the frequency of sound waves, and is measured in hertz (Hz). It can be seen in a soundwave by measuring the distance two corresponding points in the same soundwave, or the wavelength. Humans can detect between 20-20000 hertz; sounds with pitches below this are called subsonic, and sounds with pitches higher are called supersonic. Pitch determines the way a note sounds. Due to the way we perceive sounds, pitches around 4000 Hz sound the loudest to a normal humans ear. Amplitude is a measurement of the loudness of a sound. Amplitude can be seen in a soundwave by measuring the distance between the crest (top) and the trough (bottom) of a soundwave. Amplitude is measured in decibels, (dB), a logarithmic scale from 0-140. 0 decibels represents the faintest sound which is able to be heard by humans, and 140 represents the sounds which leads to hearing loss in a normal human being. Amplitude can be seen in a wavelength by Decibels and hertz, together, determine the total power output of a sound at a distance, in the following equation.
Power = intensity X sphere aura
The intensity is the strength of the sound at the source, and the sphere aura represents how far away the energy is from the source when it is received. Because the sound moves in a spherical fashion, it is decreased by its inverse square for every unit the sphere increases. Also, when comparing the same sound at a different distance, the total amount of energy will still be the same; this is because there is still the same amount of energy, but it is more or less compacted then previously. As the area covered increases, the intensity decreases. If we were to substitute it into an equation where a sound source makes an intensity of 1 x 10-3 W/m2 at 5m, the resulting equation would look like the following:
P=(1 x 〖10〗^(-3) W/m^2 )(4π(5〖m)〗^2 ) = 0.063 W
The speed of sound travelling through the air can be written as the following formula.
v=331 m/s+(0.6 (m/s)/c) (temperature)
The formula states that the velocity of sound traveling through air is equal to 331 metres per second plus 0.6 multiplied by the current air temperature in Celsius. This means that as air temperature increases, the speed of sound increases. Therefore, if the air temperature was at 10°C, the formula would look like this:
v=331 m/s+(0.6 (m/s)/C) (10°C)