# Chapter 17 : Sound

### Topics covered in this snack-sized chapter:

#### Sound arrow_upward

• Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing
• Sound plays an important role in our life. It helps us to communicate with one another.

• #### Sound is produced by a Vibrating Body arrow_upward

• The to and fro or back and forth motion of an object is termed as vibration.
• When a tightly stretched band is plucked, it vibrates and produces sound.
• When it stops vibrating, it does not produce any sound.
• We see that a vibrating object produces sound. In some cases, the vibrations are easily visible to us.
• But in most cases, their amplitude is so small that we cannot see them. However, we can feel them.

• #### Sound needs a medium for Propagation arrow_upward

• Sound needs a medium to travel.
• When air has been removed completely, it is said that there is vacuum.
• The sound cannot travel through vacuum.
• Sound can travel through any solid.
• For example, sound can travel through wood or metal.

• #### Amplitude, Time Period and Frequency of a Vibration arrow_upward

• The to and fro motion of an object is known as vibration. This motion is also called oscillatory motion.
• The number of oscillations per second is called the frequency of oscillation.
• Frequency is expressed in hertz. Its symbol is Hz.
• A frequency of 1 Hz is one oscillation per second.
• Amplitude and frequency are two important properties of any sound.
• The loudness of sound depends on its amplitude.
• When the amplitude of vibration is large, the sound produced is loud. When the amplitude is small, the sound produced is feeble.
• The frequency determines the shrillness or pitch of a sound.
• If the frequency of vibration is higher we say that the sound is shrill and has a higher pitch.
• If the frequency of vibration is lower, we say that the sound has a lower pitch.
• For example, a drum vibrates with a low frequency. Therefore, it produces a low-pitched sound.
• On the other hand, a whistle has a high frequency and therefore, produces a sound of higher pitch

• #### Audible and Inaudible Sounds arrow_upward

• The sounds of frequencies less than about 20 vibrations per second (20 Hz) cannot be detected by the human ear. Such sounds are called inaudible.
• On the higher side, sounds of frequencies higher than about 20,000 vibrations per second (20 kHz) are also not audible to the human ear.
• Thus, for human ear, the range of audible frequencies is roughly from 20 to 20,000 Hz.

• #### Noise Pollution arrow_upward

• Presence of unwanted gases and particles in air is called air pollution.
• Similarly, presence of excessive or unwanted sounds in the environment is called noise pollution.
• Major causes of noise pollution are sounds of vehicles, explosions including bursting of crackers, machines, loudspeakers etc.
• Presence of excessive noise in the surroundings may cause many health related problems.
• Lack of sleep, hypertension (high blood pressure), anxiety and many more health disorders may be caused by noise pollution.
• A person who is exposed to a loud sound continuously may get temporary or even permanent impairment of hearing.

• #### Measures to Limit Noise Pollution arrow_upward

• The noisy operations must be conducted away from any residential area.
• Noise producing industries should be set up away from such areas.
• Use of automobile horns should be minimized.
• TV and music systems should be run at low volumes.
• Trees must be planted along the roads and around buildings to cut down on the sounds reaching the residents, thus reducing the harmful effects of noise pollution.

• #### Thank You from Kimavi arrow_upward

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