Speed Of Sound

Sound waves travel through a medium by alternately contracting and expanding the parts of the medium in which it travels. The speed of sound is the distance travelled per unit time by any sound. In the next section few sections, let us learn to determine the speed of sound in various medium.

What is Speed of Sound?

The speed of sound is defined as the dynamic propagation of sound waves. This depends on the characteristics of the medium through which the propagation takes place. Speed of sound is used for describing the speed of sound waves in an elastic medium.

Speed of Sound Formula

The formula for speed of sound is given with respect to gases. It is the square root of product of coefficient of adiabatic expansion and pressure of the gas divided by the density of the medium. The mathematical representation is given as:

\(v=\sqrt{\frac{\gamma P}{\rho }}\)

Where,

  • v is the speed of sound
  • γ is the coefficient of adiabatic expansion
  • P is the pressure of the gas
  • ρ is the density of the medium

What is the Speed of Sound in Air?

The speed of sound is an essential parameter used in a variety of field in Physics. The speed of sound refers to the distance travelled per unit time by a sound wave propagating through a medium. The speed of sound in air at 20oC is 343.2 m/s which translates to 1,236 km/h.

Speed Of Sound

The speed of sound in gases is proportional to the square root of the absolute temperature (measured in Kelvin) but it is independent of the frequency of the sound wave or the pressure and the density of the medium. But none of the gases we find in real life are ideal gases and this causes the properties to slightly change.

Speed of Sound in Solid, Liquid and Gases

Sound can travel through wood too! In fact, sound likes travelling through solid more. In the olden days, doctors used stethoscopes consisting of thin wooden rods with broadened ends and they worked exactly like our modern ones and performed just as well. How can sound travel through solids?

Speed of Sound in Solid

Sound is nothing more than a disturbance which is propagated by the collisions between the particles; one molecule hitting the next and so forth. Solids are significantly denser than liquids or gases. This means that the molecules are closer to each other in solids than in liquids and in liquids than in gases. This closeness due to density means that they can collide very quickly. Effectively it takes less time for a molecule of a solid to bump into its neighbouring molecule. Due to this advantage, the speed of sound in a solid is larger than in a gas.

Speed of Sound in Liquid

Similarly, the density of a liquid is greater than the density of a gas. Therefore the distances between molecules are more in liquids than in solids but are less than in gases. Hence the speed of sound in liquids lies in between the speed of sound in solids and gases.

Speed of Sound in Gas

We should remember that the speed of sound is independent of the density of the medium when it enters a liquid or solid. Since gases expand to fill the given space, density is quite uniform irrespective of the type of gas. This clearly isn’t the case with solids and liquids.

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Table of Speed of Sound in Various Medium

The table below lists the speed of sound in various media. The proportional variation of speed with density is clearly visible here.

Speed Of Sound

The table shows the speed of sound in different materials
Another very curious fact is that in solids, sound waves can be created either by compression or by tearing of the solid also known as Shearing. Such waves exhibit different properties from each other and also travel at different speeds. This effect is seen clearly in Earthquakes. Earthquakes are created due to the movement of the earth plates which then sends these disturbances in the form of waves similar to sound waves through the earth and to the surface causing an Earthquake. Typically compression waves travel faster than tearing waves which is why Earthquakes always start with an up and down motion followed after some time by side to side motion. In seismic terms, the compression waves are called P-waves and the tearing waves are called S-waves. They are the more destructive of the two, causing most of the damage in an earthquake.

Frequently Asked Questions

Name the property used for distinguishing a sharp sound from a dull sound.

Pitch is the property which is used for distinguishing a sharp sound from a dull sound. Pitch depends on the frequency of the sound wave. Higher the frequency, higher the pitch.

Define intensity of sound.

Intensity of sound is defined as the amount of energy passing through unit area at that point. It is inversely proportional to the square of distance between the point and the source. It is also directly proportional to the square of vibration and frequency and to the density of the medium.

What are the different units of loudness?

There are three units of loudness and they are bel, decibel, and phon.

Name the medium in which the speed of sound is large.

Steel.

Name the factors on which the speed of sound in gas depends.

Speed of sound in gas depends on density and elasticity of the gas.

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