Three lives have I. I'm gentle enough to sooth the skin, light enough to float to the sky, and powerful enough to break through rock. What am I?

Here's one more.:
Romeo and Juliet were found in a room lying dead. The only funrniture is a cama and a table. Then on the floor, there broken glass and water. Outside, there's a train track. What killed romeo and Juliet?

Hint: Something very quick and powerful had to do this...what was it?