Q. Why transverse mechanical waves can not be propagated in liquids and gases ?
Ans: To transmit a transverse mechanical wave the medium must be elastic so as to provide a restoring force when acted on by shearing stress. But liquids and gases can not sustain shear stress to provide restoring force, but rather start flowing when acted on by shearing stress.
(a) All non-mechanical waves are transverse.
(b) In gases and liquids mechanical waves are always longitudinal e.g. sound waves in air and water.
(c) In solids mechanical waves can be either transverse or longitudinal depending on the mode of excitation. The speeds of the two waves in the same solid are also different.