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SS2 Third Term Physics Lesson Note – Sound Waves

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WEEK 9:

TOPIC: SOUND WAVES

CONTENTS

Sources of sound
Transmission of sound
Characteristics of sound
Forced vibrations
Solved problems

Sub topic 1: Sources of sound

Sound is a form of wave motion which is conveyed through an elastic medium from a vibrating body to a listener. It is a longitudinal wave. Sound has a number of sources including sound from animals, moving aircraft, vehicles, vibrating turning fork, e.t.c

Sound wave is also a mechanical wave. That is, it cannot travel through vacuum. There must be a material medium for its to propagate. Astronauts on the moon can only communicate each other via walkie-talkie even at close distance because there is no air molecule to propagate sound wave on the moon.

Sub topic 2: Transmission of sound

Sound waves are produced from vibrating systems and travels as a series of compressions and rarefactions as discussed earlier. Sound waves do not travel through a vacuum. It requires a material medium. Your teacher will show you a simple experiment to investigate this fact. Speed of sound varies from medium to medium because it depends on the density, elasticity and temperature of the transmitting medium. For example, the speed of sound in air is about 330m/s at 0⁰ C. in water it is about 1500 m/s. in steel rods, it can be as high as 5000m/s. wind also affect the speed of sound in relation to a listener. A louder sound is heard if the direction of travel of the wind is the same as the direction of propagation of the sound. If the two directions are opposite, the sound will decrease. In air the speed of sound increases by about 0.6m/s for each degree rise in temperature. The rise is much less in solids and liquids

As mentioned earlier, the speed of sound varies with density and the elastic properties of the medium. Experiment shows that, the velocity ‘v’ of sound is proportional to the Young’s modulus (E) of elasticity and the density, ‘d’ according to the equation:

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