What you need to get is out of there. If he smashes everything in the house, so what. It's just things. Things can be replaced.

Your life cannot. The next time that he assaults you, call the police. Get a domestic violence restraining order (be sure to include your son and mother in the restraining order and get exclusive possession of the house) AND press charges.

And don't back down. Let your son see that what his father is doing is wrong and that you can stand up to him and fight to protect both you and your son (and your mother, as well).

You need to get out for both you and your son's sake. Do you want your son to grow up to abuse his spouse? By staying, you are teaching him that abuse is okay.