Degrees of Freedom

Degrees of freedom (DOF) are a measure of how components can move relative to one another in a model. A body free in space has six DOF in which it can move: three translational and three rotational. Each DOF corresponds to at least one equation of motion.

When you add a constraint, such as a revolute joint, between two components, you remove DOF between the components, causing them to remain positioned with respect to one another regardless of any motion or force in the model. Each constraint removes different DOF.