The object of the preposition in this sentence is “track”. The prepositional phrase “around the car” is modifying the verb “is racing” so it is acting as an adverb.
Prepositional phrases are a group of words that start with a preposition, in this case “around”, followed by an object. Prepositional phrases are a part of speech that can modify nouns (adjectival phrase) or verbs (adverbial phrase).
