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MCAT Content / Sound / Relative Speed Of Sound In Solids Liquids And Gases

### Relative Speed of Sound in Solids, Liquids, and Gases

Topic: Sound

The speed of sound is dependent on the properties of the material it travels through: it will travel faster through a solid than a liquid, and faster through a liquid than a gas.

The speed of sound is the distance traveled in a unit of time by a sound wave through an elastic medium. This medium can be a solid, liquid, gas, or even plasma. The speed of sound is dependent on the properties of the media the sound is travelling through. The general value given for the speed of sound is the speed of a sound wave in air, at sea level, at normal atmospheric pressure; that number is 344 m/s. However, this number is not constant. Sound travels faster in a solid than in a liquid, and faster in a liquid that in a gas.

There are two different kinds of sound waves: compression waves and shear waves. Compression waves can travel through any media, but shear waves can only travel through solids. The speed of a compression wave is determined by the media’s compression capacity, shear modulus, and density, while the speed of the shear wave is only determined by the shear modulus and density. The shear modulus is a measurement of the elasticity or rigidity of a material. Calculating this is outside of the scope of this atom, but there are tables which tell you its value for materials.

The speed of sound is usually denoted by , and a general equation can be used to calculate it. This is called the Newton-Laplace equation:

where K is the coefficient of stiffness of the material (also called the Bulk modulus) and p is the density of the material. It is easy to see that the speed of sound will increase with stiffness and decrease with density.

One can also increase the speed of sound by increasing the temperature of the medium. The higher the temperature, the higher the kinetic energy, hence a faster speed of sound.

Practice Questions

MCAT Official Prep (AAMC)

Physics Online Flashcards Question 3

Physics Online Flashcards Question 20

Physics Question Pack Question 75

Key Points

• Sound can travel through any compressible material. These media can be solid, liquid, gas, or even plasma.

• The speed of sound is dependent on the properties of the material it travels through. It will travel faster through a solid than a liquid, and faster through a liquid than a gas.

• The general number given for the speed of sound is calculated at sea level, in air, at normal atmospheric pressure. That value is 344 m/s.

Key Terms

Elastic: The property of a material deformed under the load can regain its original dimensions when unloaded

Medium: General term for different types of materials.

Kelvin: in the International System of Units, the base unit of thermodynamic temperature; 1/273.16 of the thermodynamic temperature of the triple point of water; symbolized as K

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