Types of Work

There are many different ways that energy can be stored in a body by doing work on it: elastically by straining it, electrostatically by charging it, polarizing it in an electric field $\vec{E}$, magnetizing it in a magnetic field $\vec{H}$, chemically by changing its composition with a chemical potential $\mu$. Each example is a different type of work--they all have the form that the (differential) work performed is the change in some extensive variable of the system multiplied by an intensive variable.

Students often get confused about where to put minus signs in equations dealing with work, heat and changes in energy. This confusion can usually be removed by forming a physical picture of what is actually happening in the system and using common sense.¹