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We have learnt that vibration is necessary for producing sound. Explain why the sound produced by every vibrating body cannot be heard by us?
 
Sounds are of different frequencies, but  are being heard by human beings. So, we classify sounds into different categories.
 
(i) Audible sound -
 
(ii) Inaudible sound -
 
(iii) Infrasonic sound -
 
(iv) Ultrasound -