Generally,
social science is the study of (human)
societies, of the human (as a
social animal), and the frameworks and conditions in which humans aggregate into social structures.
Like any major disciplinary division, the borders of social science are somewhat hazy. Psychology, for instance, is a mind-medicine study, in some respects more closely related to
Biology than to, say, Geography. Disciplinary specialization is a lively aspect of our social structure, leading to cross-disciplinary studies like literary anthropology (study of cultures from their literature), accounting (mathematics of economics), etc. In
our increasingly specialized technological society, academic
subcultures flourish, such that the psychologist uses a very different
jargon-language than his economist neighbor.
Two problems of the social scientist are complexity and ethics. Social science is in its infancy, compared to "hard sciences" like chemistry, because we have incredibly exact measurements of a relatively small assortment of chemical building blocks, but we don't have the means to satisfactorily quantify (or even enumerate) the "elements" or "particles" of societies. Ethical boundaries further limit the depth of research and application in social mechanics to the voluntary and/or anonymous, where atoms and quarks are universally indifferent to their privacy and freedom.