( ( A ( bow wave ) ) ( ( is ( produced ( when ( ( a ( wave source ) ) ( ( moves ( -LRB- ( A -RRB- ) ) ) ( faster ( than ( ( the waves ) ( it generates ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT A) (NN bow) (NN wave)) (VP (VBZ is) (VP (VBN produced) (SBAR (WHADVP (WRB when)) (S (NP (DT a) (NN wave) (NN source)) (VP (VBZ moves) (PRN (-LRB- -LRB-) (NP (NNP A)) (-RRB- -RRB-)) (NP (NP (JJR faster)) (PP (IN than) (NP (NP (DT the) (NNS waves)) (SBAR (S (NP (PRP it)) (VP (VBZ generates)))))))))))) (. .)))
A bow wave is produced when a wave source moves (A) faster than the waves it generates.
(ROOT (S (NP (DT A) (NN bow) (NN wake)) (VP (VBZ is) (VP (VBN created) (SBAR (WHADVP (WRB when)) (S (NP (DT the) (NN wave) (NN source)) (VP (VBZ moves) (ADVP (RBR faster)) (PP (IN than) (NP (DT the) (NN wave) (NN propagation) (NN speed)))))))) (. .)))