Elasticity and density and velocity of transmission

NEETS MODULE 10-Wave Propagation, Transmission Lines,

and Antennas

UNCLASSIFIED

1-30

UNCLASSIFIED

1.5 ELASTICITY AND DENSITY AND VELOCITY OF TRANSMISSION

Sound waves travel through any medium to a velocity that is controlled by the medium.

Varying the frequency and intensity of the sound waves will not affect the speed of

propagation. The ELASTICITY and DENSITY of a medium are the two basic physical

properties that govern the velocity of sound through the medium.

Elasticity is the ability of a strained body to recover its shape after deformation, as from a

vibration or compression. The measure of elasticity of a body is the force it exerts to

return to its original shape.

The density of a medium or substance is the mass per unit volume of the medium or

substance. Raising the temperature of the medium (which decreases its density) has the

effect of increasing the velocity of sound through the medium.

The velocity of sound in an elastic medium is expressed by the formula:

Even though solids such as steel and glass are far more dense than air, their elasticity’s

are so much greater that the velocities of sound in them are 15 times greater than the

velocity of sound in air. Using elasticity as a rough indication of the speed of sound in a

given medium, we can state as a general rule that sound travels faster in harder materials

(such as steel), slower in liquids, and slowest in gases. Density has the opposite effect on

the velocity of sound, that is, with other factors constant, a denser material (such as lead)

passes sound slower.

At a given temperature and atmospheric pressure, all sound waves travel in air at the

same speed. Thus the velocity that sound will travel through air at 32º F (0º C) is 1,087

feet per second. But for practical purposes, the speed of sound in air may be considered

as 1,100 feet per second. Table 1-1 gives a comparison of the velocity of sound in various

mediums.