( ( When ( ( two ( billiard balls ) ) ( collide ( the collision ) ) ) ) ( ( is ( nearly elastic ) ) . ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (CD two) (JJ billiard) (NNS balls)) (VP (VBP collide) (NP (DT the) (NN collision))))) (VP (VBZ is) (ADJP (RB nearly) (JJ elastic))) (. .)))
When two billiard balls collide the collision is nearly elastic.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NN gas) (NNS particles)) (VP (VBP collide)))) (, ,) (NP (DT these) (NNS collisions)) (VP (VBP are) (VP (VBN considered) (S (ADJP (JJ elastic))))) (. .)))