( ( Waves ( which ( require ( ( any medium ) ( for ( their propagation ) ) ) ) ) ) ( ( are ( called ( mechanical waves ) ) ) . ) )
(ROOT (S (NP (NP (NNS Waves)) (SBAR (WHNP (WDT which)) (S (VP (VBP require) (NP (NP (DT any) (NN medium)) (PP (IN for) (NP (PRP$ their) (NN propagation)))))))) (VP (VBP are) (VP (VBN called) (NP (JJ mechanical) (NNS waves)))) (. .)))
Waves which require any medium for their propagation are called mechanical waves.
(ROOT (S (NP (JJ Mechanical) (NNS waves)) (VP (VBP require) (NP (NP (DT a) (NN material) (NN medium)) (PP (JJ such) (IN as) (NP (NP (NN water)) (, ,) (NP (NN air)) (, ,) (CC or) (NP (NN rope)))))) (. .)))