( This ( greatly ( ( reduces ( sliding friction ) ) . ) ) )
(ROOT (S (NP (DT This)) (ADVP (RB greatly)) (VP (VBZ reduces) (S (VP (VBG sliding) (NP (NN friction))))) (. .)))
This greatly reduces sliding friction.
(ROOT (S (NP (VBG Sliding) (NN friction)) (VP (VBZ is) (NP (NP (NN friction)) (SBAR (WHNP (WDT that)) (S (VP (VBZ acts) (PP (IN on) (NP (NP (NNS objects)) (SBAR (WHADVP (WRB when)) (S (NP (PRP they)) (VP (VBP are) (VP (VBG sliding) (PP (IN over) (NP (DT a) (NN surface)))))))))))))) (. .)))