How does the relationship between Prospero and Ariel differ between Act 1, Scene 2 and Act 5, Scene 1?
In Act I scene 2 the relationship is more straightforward: Prospero is master and Ariel is servant. When Ariel pushes, reminding Prospero of the promise of liberty, he essentially shuts Ariel down.
By contrast, in Act V scene 1, the relationship is much more affectionate, and much more one of equals, or at least near-equals. Ariel speaks of what a human would feel, and the emphasis is on emotions, rather than power and hierarchy (and, of course, Prospero frees Ariel at the end of the play).