( ( that is ) ( , ( ( ( the impulse ) ( ( is always ) ( equal ( to ( the ( momentum change ) ) ) ) ) ) . ) ) )
(ROOT (S (INTJ (DT that) (VBZ is)) (, ,) (S (NP (DT the) (NN impulse)) (VP (VBZ is) (ADVP (RB always)) (ADJP (JJ equal) (PP (TO to) (NP (DT the) (NN momentum) (NN change)))))) (. .)))
that is, the impulse is always equal to the momentum change.
(ROOT (S (NP (NP (NNP Change)) (PP (IN in) (NP (NP (NN momentum)) (PP (IN in) (NP (DT an) (NN object)))))) (VP (VBZ is) (ADJP (JJ equivalent) (PP (TO to) (NP (NN impulse))))) (. .)))