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What is it ?
The frequency of a sound is the measurement of the number of cycles per second of a sound wave. When a sound source produces sound, it creates vibrations in the air (or any other medium) that propagate as sound waves. The frequency of a sound is the number of complete cycles of these vibrations that occur in one second. The higher the frequency, the higher the sound, and the lower the frequency, the lower the sound. Frequency is measured in Hertz (Hz), which is the unit of frequency measurement. One Hertz represents one vibration per second. For example, a frequency of 1000 Hz corresponds to 1000 vibrations per second. The first research concerning sound phenomena dates from the 6th century BC with the Pythagorean school which studied the functioning of vibrating strings and built a musical scale. The description of the first absolute determination of the frequency of a pure audible sound proposed by Mersenne in his Universal Harmony (1637). Mersenne also made the first calculations of the speed of sound. It was the German physicist and mathematician Christian Johann Doppler who was the first to suggest that the frequency of a sound could be modified by the movement of the source or the observer. This led to the Doppler effect, which bears his name and is now widely used in many applications, including meteorology and medicine. Physicist Lord Rayleigh developed the theory that now bears his name, known as Rayleigh's theory. This theory describes how sound waves propagate in a medium and how they are affected by different factors such as density and air pressure.
A smartphone is the ideal tool to study frequencies and sound waves. The following activies can be done in class or as home assignment :
Measure the wavelength and deduce the frequency of a sound using FizziQ's oscilloscope : https://www.fizziq.org/en/team/music-scale
What is a music scale and what are the freqeuncies of notes within a scale : https://www.fizziq.org/en/team/music-scale
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