Once joints have been defined, it is necessary to specify the various conditions that are imposed upon the joints to simulate the physical environment in which they operate. To specify conditions, add properties to the various types of joints and set the initial conditions including any forces, torques, or imposed motion. You must also define any external forces, such as gravity, that affect the simulation.
There are tools to help define the physical environment, such as the input grapher and special mouse behaviors that assist in quickly defining and refining the property values.