As a teacher, I have observed students in my classes being so engrossed and absorbed in what they are doing that they do not notice the time that is passing. When I hear someone say, "Oh, we are already done!" or "The class is already over?", this is an indication to me that they have not been aware of the time as it was passing. It is precisely this unawareness of time passing that we attempt to capture by using the construction of the verb "to be" with the past participle of the verbs "engross' or "absorb". We can think of the students to be in a state where they do something, like conducting a science investigation but where they are not aware of the situation as such.