( ( recognizes ( that ( ( forces ( of ( ( ( ( ( gravity , ) magnetism ) , ) and ) electricity ) ) ) ( operate ( simple machines ) ) ) ) ) . )
(ROOT (S (VP (VBZ recognizes) (SBAR (IN that) (S (NP (NP (NNS forces)) (PP (IN of) (NP (NP (NN gravity)) (, ,) (NP (NN magnetism)) (, ,) (CC and) (NP (NN electricity))))) (VP (VBP operate) (NP (JJ simple) (NNS machines)))))) (. .)))
recognizes that forces of gravity, magnetism, and electricity operate simple machines.
(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.