Ans 1.) Sound reaches our ears in the form of transverse  waves or vibrations  from its source of production.

Ans 2.)Sound travels by itself mostly through its medium of transportation but at times sound is produced by force and these sound vibrations are called forced vibrations.For example- with the help of an amplifier. 

Ans 3.)Sound is a form of energy.

Ans 4.)We hear sound even when we close our ears but its magnitude and frequency is very less due to the obstruction of our hands.It also depends upon the frequency and loudness of the sound.

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