The force package contains a complete physics simulation engine for using physical force calculations to layout and animate graph elements. Force simulations consist of a series of force functions that calculate forces acting on various graph elements, and an integrator that determines how these calculated forces effect the position and velocity of these elements over time. The ForceSimulation class keeps track of which elements should be included in the simulation, as well as which force functions and integrator are used. To create your own custom simulations, create a new ForceSimulation instance and add the desired force functions. Custom force functions can be introduced by subclassing AbstractForce or implementing the Force interface. Additionally, the ForcePanel user interface component can be used during development to explore different parameterizations of the various force functions until a desired behavior is found.