Notes On Characteristics of Sound - CBSE Class 8 Science
Sound is a form of energy produced by a vibrating bodies. Sound requires a material medium for its propagation. Sound does not propagate in vacuum as there is no material in the vacuum. The to and fro or back and forth motion of an object is called vibration. Some instruments produce sound due to the vibration of membranes, some due to the vibration of strings, and some others produce sound due to the vibration of an air column. Amplitude The maximum displacement of a vibrating particle from its mean or equilibrium position is called its amplitude. Time period The time taken by the vibrating particle for one full vibration or oscillation is called the time period of vibration. Frequency The number of vibrations per second is called the frequency. Frequency is measured hertz (Hz). Characteristics of Sound Sound produced by any means has the following characteristics, namely, loudness, pitch or shrillness, and quality or timbre. Loudness The loudness of sound depends on its amplitude. The loudness of sound is proportional to the square of the amplitude. A roar of a lion is louder than a woman’s voice. The loudness of sound is measured in Decibel (db). If loudness exceeds 80 db, then the sound becomes physically painful. Pitch The pitch of sound depends on its frequency. If frequency is more, then the pitch or shrillness is more. The pitch of a woman’s voice is more and it is shriller then a man’s voice. Audible sound Not all sound produced by vibrating bodies is audible. The human ear can recognise the sounds of frequencies in the range of 20 Hz to 20,000 Hz. This range of frequency of sound is called audible sound. Some animals like dogs and snakes can hear sounds of frequencies greater than 20,000 Hz. Infrasonic sounds Sounds of frequencies less than 20 Hz are called infrasonic sounds. Ultrasonic sounds The sounds of frequencies greater than 20,000 Hz are called ultrasonic sounds.

#### Summary

Sound is a form of energy produced by a vibrating bodies. Sound requires a material medium for its propagation. Sound does not propagate in vacuum as there is no material in the vacuum. The to and fro or back and forth motion of an object is called vibration. Some instruments produce sound due to the vibration of membranes, some due to the vibration of strings, and some others produce sound due to the vibration of an air column. Amplitude The maximum displacement of a vibrating particle from its mean or equilibrium position is called its amplitude. Time period The time taken by the vibrating particle for one full vibration or oscillation is called the time period of vibration. Frequency The number of vibrations per second is called the frequency. Frequency is measured hertz (Hz). Characteristics of Sound Sound produced by any means has the following characteristics, namely, loudness, pitch or shrillness, and quality or timbre. Loudness The loudness of sound depends on its amplitude. The loudness of sound is proportional to the square of the amplitude. A roar of a lion is louder than a woman’s voice. The loudness of sound is measured in Decibel (db). If loudness exceeds 80 db, then the sound becomes physically painful. Pitch The pitch of sound depends on its frequency. If frequency is more, then the pitch or shrillness is more. The pitch of a woman’s voice is more and it is shriller then a man’s voice. Audible sound Not all sound produced by vibrating bodies is audible. The human ear can recognise the sounds of frequencies in the range of 20 Hz to 20,000 Hz. This range of frequency of sound is called audible sound. Some animals like dogs and snakes can hear sounds of frequencies greater than 20,000 Hz. Infrasonic sounds Sounds of frequencies less than 20 Hz are called infrasonic sounds. Ultrasonic sounds The sounds of frequencies greater than 20,000 Hz are called ultrasonic sounds.

#### Activities

 Activity 1 amrita.olabs.co.in has developed an interactive animation to simulate the laws of reflection of sound. Using it we can understand that the angle of incidence is equal to the angleof reflection of sound. Go to Activity Activity 2 iknowthat.com has developed an interactive animation to simulate the production and propagation of sound in a mechanical medium. This simulatiion explores pitch and volume of sound. Go to Activity

Next