( But ( ( the surface ) ( ( ( does not ) ( affect ( ( the ( sliding friction ) ) ( of ( a body ) ) ) ) ) . ) ) )
(ROOT (S (CC But) (NP (DT the) (NN surface)) (VP (VBZ does) (RB not) (VP (VB affect) (NP (NP (DT the) (JJ sliding) (NN friction)) (PP (IN of) (NP (DT a) (NN body)))))) (. .)))
But the surface does not affect the sliding friction of a body.
(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)))))))))))))) (. .)))