( Sound ( ( ( ( ( ( needs ( ( a medium ) ( -LRB- ( ( such ( as air ) ) -RRB- ) ) ) ) ( to travel ) ) , ) and ) ( is ( ( a ( longitudinal wave ) ) ( of ( pressure ( in ( the medium ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Sound)) (VP (VP (VBZ needs) (NP (NP (DT a) (NN medium)) (PRN (-LRB- -LRB-) (PP (JJ such) (IN as) (NP (NN air))) (-RRB- -RRB-))) (S (VP (TO to) (VP (VB travel))))) (, ,) (CC and) (VP (VBZ is) (NP (NP (DT a) (JJ longitudinal) (NN wave)) (PP (IN of) (NP (NP (NN pressure)) (PP (IN in) (NP (DT the) (NN medium)))))))) (. .)))
Sound needs a medium (such as air) to travel, and is a longitudinal wave of pressure in the medium.
(ROOT (S (NP (NNP Medium)) (VP (VBZ is) (NP (NP (DT the) (NN matter)) (SBAR (WHPP (IN through) (WHNP (WDT which) (NN sound))) (S (NP (NNS waves)) (VP (VBP travel)))))) (. .)))