( ( ( The position ) ( of ( ( ( ( ( the magnet ) ( with ( respect ( to ( the door ) ) ) ) ) ( -LRB- ( ( for ( ( the force ) ( produced ( by ( the magnet ) ) ) ) ) -RRB- ) ) ) or ) ( the ground ) ) ) ) ( ( -LRB- ( ( for ( ( the force ) ( of gravity ) ) ) -RRB- ) ) ( ( must ( ( change ( for energy ) ) ( to ( be ( ( lost or ) gained ) ) ) ) ) . ) ) )
(ROOT (S (NP (NP (DT The) (NN position)) (PP (IN of) (NP (NP (NP (DT the) (NN magnet)) (PP (IN with) (NP (NP (NN respect)) (PP (TO to) (NP (DT the) (NN door)))))) (PRN (-LRB- -LRB-) (PP (IN for) (NP (NP (DT the) (NN force)) (VP (VBN produced) (PP (IN by) (NP (DT the) (NN magnet)))))) (-RRB- -RRB-)) (CC or) (NP (DT the) (NN ground))))) (PRN (-LRB- -LRB-) (PP (IN for) (NP (NP (DT the) (NN force)) (PP (IN of) (NP (NN gravity))))) (-RRB- -RRB-)) (VP (MD must) (VP (VB change) (PP (IN for) (NP (NN energy))) (S (VP (TO to) (VP (VB be) (VP (VBN lost) (CC or) (VBN gained))))))) (. .)))
The position of the magnet with respect to the door (for the force produced by the magnet) or the ground (for the force of gravity) must change for energy to be lost or gained.
(ROOT (S (NP (NNP Gravity) (CC and) (NNP magnetism)) (VP (VBP are) (NP (DT both) (JJ common) (NNS forces))) (. .)))
Gravity and magnetism are both common forces.