Physical and social sciences are two large categories that each include a variety of fields and each are concerned with scientific description of observable phenomena. The approach each takes in that pursuit and the phenomena each chooses to study differentiates the two as separate methods with different conceptions of observable reality. The two have different objects of study, methodology and experimental philosophies, yet the boundaries between the two are not always clear.
Objects of Study
Generally speaking, the object of physical science research is to study physical phenomena in their concrete reality, without being concerned with cultural context. Natural sciences like chemistry and physics study the physical behavior of objects such as cars in motion or acid solutions. Social sciences like anthropology and economics, however, tend to ask questions about the social context in which those objects find themselves, assuming that social forces like supply and demand or cultural affinity are more likely to explain how the world works than natural laws. In response to a research problem involving numerous deaths in automobile accidents, for instance, a physicist might study the behavior of bodies in motion upon collision in order to build safer automobiles, whereas an anthropologist might study the motivations for speeding to design effective anti-speeding campaigns.
The scientific method, the approach of repeated trials until a pattern is discovered or another conclusion can be proven false, is the basis of physical sciences. In fact, the development of the natural sciences relies on repeated laboratory testing of hypotheses, the reproducibility of results and the constant challenging of established laws and theories. Experimental data is turned into theories and laws about the way the world operates and theories are used to predict future observations until laboratory testing manages to produce a different result. Using a different approach, the social sciences tend to collect experiential data to establish a broad social phenomenon. The inability to place all of society in a laboratory creates an experiential methodology where the results or observations of changing phenomena are not as easily reproduced in a laboratory.
The methodology that natural sciences use is fairly straightforward: an experimental observation is abstracted to a natural constant like a law – water, for example, boils at 100 degrees Celsius -- and this is then used to describe and predict natural phenomena until the hypothesis can be disproved. Natural sciences assume that every molecule of water will behave like every other molecule of water in accordance with this rule, which is a methodology highly criticized by social scientists who begin with the assumption that they are studying complex and changing social phenomena that can only be described in a specific place and time. Human beings, as members of a social unit, have certain characteristics of the collective, but also respond to personal traits and characteristics drawn from other cultures. As a result, social scientists use methods like field observation, data collection and focus groups to generate positions and theories, acknowledging that a similar study at another time may produce different results.
Complexity and Interdisciplinary Study
While physical and social sciences are often described as two exclusive categories, the reality is that each draws from certain approaches and methodologies of the other. Economics, for example, a social science, includes both research using traditional social science methods like interviews and focus groups to predict consumer behavior and studies using complex mathematical modeling more reminiscent of physics or chemistry. Similarly, the study of ecology, a physical science, recognizes that its object of study is involved in such a complex web of ecosystem inter-dependencies that it is often forced to use sampling methods innovated by the social sciences in order to begin to make sense of a complex situation.