( Nature ( ( requires ( that ( these ( ( ( equipotential lines ) ( -LRB- ( or ( surfaces -RRB- ) ) ) ) ( be ( perpendicular ( to ( ( the ( electric ( field lines ) ) ) ( that ( produce them ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Nature)) (VP (VBZ requires) (SBAR (IN that) (S (NP (DT these)) (VP (VP (VBP equipotential) (NP (NNS lines))) (PRN (-LRB- -LRB-) (CC or) (VP (VBZ surfaces)) (-RRB- -RRB-)) (VP (VB be) (ADJP (JJ perpendicular) (PP (TO to) (NP (NP (DT the) (JJ electric) (NN field) (NNS lines)) (SBAR (WHNP (WDT that)) (S (VP (VBP produce) (NP (PRP them))))))))))))) (. .)))
Nature requires that these equipotential lines (or surfaces) be perpendicular to the electric field lines that produce them.
(ROOT (S (SBAR (IN Since) (S (NP (DT the) (JJ electric) (NN field) (NNS lines)) (VP (VBP point) (ADVP (RB radially)) (ADVP (RB away) (PP (IN from) (NP (DT the) (NN charge))))))) (, ,) (NP (PRP they)) (VP (VBP are) (ADJP (JJ perpendicular) (S (VP (TO to) (VP (VB equipotential) (NP (NNS lines))))))) (. .)))