Pour fait court c'est la même chose, y a pas de différence, mais le mot le plus employé reste "parce que" et "car" est plus utilisé à l'écrit

Parce Que: Parce que introduces a cause. It's also less formal and more universally accepted as the English equivalent of because. Parce que has the ability to start a sentence, something you can't do with car. La pomme? Je l'ai mangée parce que j'avais faim. The apple? I at it because I was hungry. Parce qu'elle est mignonne, elle gagne plus que Pauline. Because she is cute, she earns more than Pauline. Car: Car is a justification or explanation of something. It is definitely more formal than parce que and is written more than spoken. In English this could be translated into for or because. Méfie-toi car il est violent. Be wary for he is violent. http://www.frenchcrazy.com/2013/04/the-difference-between-parce-que-and-car.html