( ( Since momentum ) ( ( ( is ( mass ( ( ( times velocity ) ( , ( and ( not mass ) ) ) ) times ) ) ) ( ( speed , ) ( direction matters ) ) ) . ) )
(ROOT (SINV (PP (IN Since) (NP (NN momentum))) (VP (VBZ is) (NP (JJ mass) (UCP (PP (CC times) (NP (NN velocity))) (, ,) (CC and) (RB not) (ADJP (JJ mass))) (NNS times))) (NP (NP (NN speed)) (, ,) (NP (NN direction) (NNS matters))) (. .)))
Since momentum is mass times velocity, and not mass times speed, direction matters.
(ROOT (S (NP (NNP Momentum)) (VP (VBZ is) (ADJP (RB directly) (VBN related) (PP (TO to) (NP (NP (DT both) (NN mass)) (CC and) (NP (NN velocity)))))) (. .)))