Phrasal verbs, also called two-word verbs, are idiomatic expressions wherein the second element of the verb (the adverb or particle) is not necessarily predictable.
Meaning / Example:
1. to pass by, rotating, as a wheel or a ball; to move past, rolling on wheels. > The wheel of a car rolled by, all by itself. It must have come off a car somewhere down the road. > The traffic rolled by relentlessly.
2. to move (past), as if rolling. > The years rolled by, and soon the two people were old and gray.