Cultural Anthro studies human cultures and everything about the culture. Physical Anthropology also believes that much of what people do can be traced back to some sort of evolutionary or instinctual cause and effect.
Sociology studies societies and groups of people, not necessarily a culture. They look at statistics, polls, surveys, etc. They believe that most of what people do can be traced back to a societal cause and effect.
For example, a man kills his wife. A cultural anthro may see it as part of that man's cultural traditions/practices to be normal, a physical anthropologist may wonder if there is an ancient gene that can explain the urge to commit a crime within our species. A sociologist will think that because of society, the man's upbringing, hardships, etc. the man killed his wife. They have two different ways of thinking.
I'm an Anthropology major.