the sound In physics, sound is a longitudinal mechanical wave . Mechanical waves are waves that travel through physical media ...
the sound
In physics, sound is a longitudinal mechanical wave . Mechanical waves are waves that travel through physical media , and they cannot propagate without the presence of a physical medium. Depending on how they propagate, the waves can be classified into two types; Longitudinal waves whose direction of propagation is parallel to the direction of vibration, and transverse waves whose direction of propagation is perpendicular to the direction of their oscillation. The sound can be defined as the vibration originating and carrying on physical media (such as air or water ) to move through it, and if the sound reaches a future such as the human ear, it can be perceived through the sense of hearing.
The origin of the sound
In order to be able to understand in a simple way the mechanism by which sound arises, it is possible to use a stringed instrument (that is, it is played by moving strings) such as a guitar. When playing the guitar, it is done by striking the strings, which causes it to vibrate up and down the equilibrium position (the equilibrium position is the original position of the string). This vibration causes the air molecules to be pushed, which will lead to a decrease in the air pressure near the string And also, it will lead to an increase in the air pressure in the new area in which the air has become, and the air molecules will push other particles, causing another decrease in the air pressure, followed by a rise in the air pressure, and by repeating this process the sound arises.And it travels through the air to the listener's ear. The area of low pressure is called rarefaction, while the area of high pressure is called compression. Thus, it can be said that sound waves are nothing but a series of compressions separated by rarefactions.
The speed of sound
In all physical media, the speed of sound depends mainly on some properties such as inertial properties, properties related to elasticity, and elastic properties contribute to the greatest influence on the speed of sound; Whereas, the more the molecules and atoms of the substance interact with each other, the higher the speed of sound in this material medium, and because of this, the speed of sound is the greatest possible in solid (p ) solid media , while it is the least possible in gaseous (p gaseous ) and in media Liquid is the speed of sound ( liquid p ) between its velocity in solid and gaseous media.
Solid p > liquid p> p gaseous
Inertial properties are dominant only when we compare the speed of sound in one phase (such as comparing the speed of sound in two different gases). Density, the speed of sound increases as the density decreases. So the speed of sound will be the greatest possible in less dense media. If we compare the speed of sound in helium gas and the speed of sound in air, we will find that the speed of sound in helium gas is the largest due to the lower density of helium compared to air.
The speed of sound in air
The speed of sound in air depends mainly on the temperature of the air, and also secondly on the percentage of humidity in the air (water vapor in the air); As the ratio of water vapor in the air controls an inertia characteristic of the medium on which the sound wave will carry, which is the density , and we have already talked about it in this article. One of the factors that strongly influence the speed of sound is temperature. Because it will affect the interaction of the molecules of the medium with each other, and this is one of the properties of elasticity that greatly affects the speed of sound.
The speed of sound in dry air at normal atmospheric pressure can be calculated according to the following relationship:
P = 331 + (0.6 x d)
Where (p) is the speed of sound, and (d) is the temperature of the air, and from this relationship it is possible to predict the speed of sound in air under standard conditions (normal atmospheric pressure, temperature 20 ° C) as the speed of sound in these conditions will equal 343 m / Th.
Calculate the speed of sound
In general, the speed of anything can be calculated by knowing the distance it travels in a given time, or in more mathematical words, the speed can be calculated by dividing the distance traveled by the time taken to cover this distance. This method also applies to sound waves, but in order for the matter to be completely clear it is necessary to talk about two important characteristics of the properties of waves , and these two properties are wavelength and frequency.
First of all, the wavelength is the distance between any two similar points on the wave in succession, such as we say the distance between two consecutive peaks or troughs in a row, as this distance is the wavelength, and the wavelength is measured in units of length, so if we are talking about wavelength in the global system of units , the unit used You will be a meter. It should be noted that a full wavelength is a full wave. While frequency is the number of waves that cross a point in a unit of time, and the frequency is equivalent to the inverse of time, which is measured in units of 1 / s, or the so-called hertz.
Since the wavelength is a distance, and the frequency is the inverse of time, when these two quantities are multiplied by each other we will get the wave velocity (because we got a distance divided by time, and this is the definition of velocity), and this can be written mathematically as follows:
P = λ × v d
Where (p) is the wave velocity, () is the wavelength, and (t d ) is the frequency of that wave.
The speed of sound can be calculated by relying on the Newton-Laplace equation, which tells us that by dividing the volume parameter by the density of the medium, we will get the square of the speed of sound in this medium, and the Newton-equation is given. Laplace is as follows:
P 2 = m h / ρ
Since (p 2 ) is the speed of sound in the middle, and (m h ) is the coefficient of volume, and (ρ) is the center density.
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