( ( These ( four forces ) ) ( ( are ( called ( lift ( , ( weight ( , ( ( thrust and ) drag ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT These) (CD four) (NNS forces)) (VP (VBP are) (VP (VBN called) (NP (NN lift) (, ,) (NN weight) (, ,) (NN thrust) (CC and) (NN drag)))) (. .)))
These four forces are called lift, weight, thrust and drag.
(ROOT (S (NP (NNP Thrust)) (VP (VBZ is) (NP (NP (DT the) (NN force)) (VP (VBG pushing) (NP (DT a) (NN rocket))))) (. .)))