a momentum that never lets up 
(ROOT (NP (NP (DT a) (NN momentum)) (SBAR (WHNP (WDT that)) (S (ADVP (RB never)) (VP (VBZ lets) (PRT (RP up)))))))
(ROOT (NP (NP (DT ) (NN )) (SBAR (WHNP (WDT )) (S (ADVP (RB )) (VP (VBZ ) (PRT (RP )))))))