( ( In ( a gas ) ) ( , ( ( as ( we ( have said ) ) ) ( , ( there ( ( ( ( is ( ( mostly empty ) space ) ) , ) ( with ( ( the molecules ) ( ( ( hurtling ( through ( that space ) ) ) and ) ( colliding ( with ( one another ) ) ) ) ) ) ) . ) ) ) ) ) )
(ROOT (S (PP (IN In) (NP (DT a) (NN gas))) (, ,) (SBAR (IN as) (S (NP (PRP we)) (VP (VBP have) (VP (VBD said))))) (, ,) (NP (EX there)) (VP (VBZ is) (NP (ADJP (RB mostly) (JJ empty)) (NN space)) (, ,) (PP (IN with) (S (NP (DT the) (NNS molecules)) (VP (VP (VBG hurtling) (PP (IN through) (NP (DT that) (NN space)))) (CC and) (VP (VBG colliding) (PP (IN with) (NP (CD one) (DT another)))))))) (. .)))
In a gas, as we have said, there is mostly empty space, with the molecules hurtling through that space and colliding with one another.
(ROOT (S (PP (IN Within) (NP (DT a) (NN substance))) (, ,) (NP (NP (NNS atoms)) (SBAR (WHNP (WDT that)) (S (VP (VP (VBP collide) (ADVP (RB frequently))) (CC and) (VP (VBP move) (ADVP (RB independently)) (PP (IN of) (NP (CD one) (DT another)))))))) (VP (VBP are) (ADJP (ADJP (RBS most) (JJ likely)) (PP (IN in) (NP (DT a) (NN gas)))))))