( ( ( ( ( The surface ) ( is fixed ) ) and ) ( there ( is ( friction ( between ( sliding ( ( mass and ) surface ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (DT The) (NN surface)) (VP (VBZ is) (VP (VBN fixed)))) (CC and) (S (NP (EX there)) (VP (VBZ is) (NP (NP (NN friction)) (PP (IN between) (S (VP (VBG sliding) (NP (NN mass) (CC and) (NN surface)))))))) (. .)))
The surface is fixed and there is friction between sliding mass and surface.
(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)))))))))))))) (. .)))