The biggest difference between Acts 1 and 2 in the play is the reversal of fortune for Pozzo and Lucky. Whereas Pozzo was clearly the master and Lucky was his slave in Act 1, in Act 2 Pozzo is blind and Lucky mute. They have become dependant on each other for survival.
For Vladimir and Estragon, each new day, seems to be just that, new. Pozzo and Lucky do not remember meeting them the day before and the boy who delivers the message that Godot will not be there but to come again tomorrow, also does not remember them. Their own long term memories seem fuzzy.
Another interesting change is that the tree now has a leaf. Is it actually the next day as in 24 hours later or has time passed and each day is like the day before? Time itself does not necessarily have the same meaning for these people as it does for us. Time is indeed relative
Although one essential point of the play, and one to which the characters return multiple times in dialogue, is that waiting is monotonous and little changes in the bleak and desolate setting of the play, we can in fact observe one major and a few minor changes.
The first minor but nonetheless significant change is one found in the stage directions. In the first act, the tree is bare of leaves, but in the second act, leaves have appeared. This might just suggest a change of season, but it also could be an emblem of hope.
The major change is in the relationship of Pozzo and Lucky. In the first act, Pozzo is a master and Lucky a slave, and Pozzo seems to almost sadistically mistreat Lucky. In the second act, Lucky, who talked fluently in the first act, is now mute and Pozzo blind, and the mutual dependence inherent in the master-slave relationship has become fully realized in Pozzo's newfound dependence on Lucky.