Sound waves can also travel trough liquids and solids. The velocity of a sound wave depends on the temperature of the medium and its elasticity (more elasticity means that molecules will move easily). Through air, sound waves travel at 343 m/s. Actually, sound waves move faster through liquids and solids than through gases.
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The human ear is able to feel frequencies between 20 Hz to 15 000 Hz, depending on the age of the person. Sound waves with a frequency above 20 000 Hz are called ultrasonic waves.
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Scientists measure the amplitude in atmospheres. Humans can detect from less than a billionth of an atmosphere to values one million times higher. However, it is hard to deal with this huge range of different values. Instead, the pressure is measured by the intensity of the sound. The quietest sound corresponds to a value of zero decibels (unit of sound intensity) and a value above a hundred corresponds to annoying sounds.
Example: A sound wave with a wavelength of 1.24 m is moving at 343 m/s. What is the frequency of this wave? wl = wavelength wl = 1.24 m v = 343 m/s
v = (wl)f f = v/wl = (343 m/s)/(1.24 m) = 276.61 Hz
When two or more waves with the same frequency reach the ear, the ear interprets these waves as one wave with amplitude as big as the sum or difference of the initial waves.
(2:1) Octave
On the other hand, an unpleasant sound or noise will be produced if the frequencies have ratios others than small whole numbers. This is called dissonance.
The sound that reaches John's ear has a higher pitch than the sound that reaches Bob's ear. This effect is called Doppler effect.
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