When the story begins, what are the forces acting upon Montag?
It would help our analysis if we specify whether we are talking about Montag at the very moment the story begins, or at the general "beginning," which includes his first conversations with Clarisse and the seeds of doubt that she inadvertently plants, particularly with her question, "Are you happy?"
At the very start, I would say that Montag generally has three forces acting on him: his job, his wife, and society.
Montag's job is probably the most satisfying thing in his life; he takes pleasure in having a stable job that also forms one of the cornerstones of his society, one which fundamentally differentiates it from our own. He sees beauty and emotion in his work, yet treats the human aspects of it with distance and a sterile tone; when burning the old woman's books he makes a brief mention of it being "janitorial work," hurting only things, not people. This same justification suggests that Montag does still need, in some way, the assurance that his job is "right."
Montag's wife, Mildred, exerts a somewhat monotonous and ineffectual force; she is his wife largely by virtue of cohabitation and name. Their marriage is dispassionate but not antagonistic; it simply exists. It is partially this weak and numbing consistency that makes Montag's "awakening" that much more pronounced, as he has become accustomed to having little passion or variation in his daily interactions with the person who is supposed to care about him the most.
Finally, Montag's society presents an image of sleekness and efficiency, but this masks an underlying disquiet. There is definitely a social force on Montag, and everyone else, to buy products, to seek comfort, and to avoid critical thought. This force becomes more and more recognizable to Montag as he begins to question it.