In these examples, down and back are not prepositions but function as adverbs to extend or change the meaning of the verb. This combination of verb and adverb is always known as a phrasal verb.

“Slowly” is an adverb here as it describes how fast the train is moving. Oh, here is a group of passengers, waiting "patiently" for their train. "Patiently" is the word describing the verb ...

“Slowly” is an adverb here as it describes how fast the train is moving. Oh, here is a group of passengers, waiting "patiently" for their train. "Patiently" is the word describing the verb ...