Social psychology is the science that studies individual beliefs, attitudes, and behaviours in settings where other people are present (or merely implied or imagined -- which makes the definition pretty broad). Notice the focus is quite different from sociology, where groups of people are studied, but closer to psychology, where individuals are studied. The focus of social psychology is the individual within the group. As such, it is an ideal venue for studying those forces that change humans -- their beliefs, their attitudes, and their behaviours.