( ( A satellite ) ( ( ( is ( subject ( to ( ( many forces ) ( besides ( the two ) ) ) ) ) ) ( we ( have ( ( discussed ( so far ) ) ( -LRB- ( ( earth ( 's ( ( ( gravity , ) and ) ( atmospheric drag ) ) ) ) -RRB- ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT A) (NN satellite)) (VP (VBZ is) (ADJP (JJ subject) (PP (TO to) (NP (NP (JJ many) (NNS forces)) (PP (IN besides) (NP (DT the) (CD two)))))) (SBAR (S (NP (PRP we)) (VP (VBP have) (VP (VBN discussed) (ADVP (RB so) (RB far)) (PRN (-LRB- -LRB-) (S (NP (NN earth)) (VP (VBZ 's) (NP (NP (NN gravity)) (, ,) (CC and) (NP (JJ atmospheric) (NN drag))))) (-RRB- -RRB-))))))) (. .)))
A satellite is subject to many forces besides the two we have discussed so far (earth's gravity, and atmospheric drag).
(ROOT (S (NP (NP (NNS Objects)) (PP (IN on) (NP (NN earth)))) (VP (VBP have) (NP (NP (CD two) (NNS forces)) (VP (VBG acting) (PP (IN on) (NP (PRP them))) (PP (IN at) (NP (DT all) (NNS times)))))) (. .)))