The appropriate physics interface for modeling a system is first chosen from the Model Wizard. The wizard includes physics branches, AC/DC, Acoustics, Chemical Species Transport, Fluid Flow, Heat Transfer, Structural Mechanics, and Mathematics, as well as the core physics interfaces included with COMSOL Multiphysics (Electrostatics, for example). The Heat Transfer in Fluids, Laminar Flow, and Transport of Diluted Species interfaces are also included in the base package but have increased functionality with this module. See the COMSOL Multiphysics Reference Manual for details pertaining to the base package.

When one or several physics interfaces are chosen from the Model Wizard (or if you open the Add Study window), you select an analysis type (stationary, dynamic, or parametric) and then the modeling interfaces are available as a nodes in the Model Builder along with all the other nodes required for modeling (Definitions, Geometry, and so forth).

By adding another physics interface, you can account for a phenomenon not previously described in a model. To do this, right-click a Component node in the Model Builder to open the Add Physics window. You can do this at any stage during the modeling process. This action still retains the existing geometry, equations, boundary conditions, and current solution, which you can build upon for further development of the model.