( ( Equipotential lines ) ( ( ( are always ) ( perpendicular ( to ( ( ( ( ( field lines ) , ) and ) therefore ) ( perpendicular ( to ( ( the force ) ( experienced ( by ( ( a charge ) ( in ( the field ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Equipotential) (NNS lines)) (VP (VBP are) (ADVP (RB always)) (ADJP (JJ perpendicular) (S (VP (TO to) (VP (VP (VB field) (NP (NNS lines))) (, ,) (CC and) (ADVP (RB therefore)) (VP (VB perpendicular) (PP (TO to) (NP (NP (DT the) (NN force)) (VP (VBN experienced) (PP (IN by) (NP (NP (DT a) (NN charge)) (PP (IN in) (NP (DT the) (NN field)))))))))))))) (. .)))
Equipotential lines are always perpendicular to field lines, and therefore perpendicular to the force experienced by a charge in the field.
(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))))))) (. .)))