**Rigid Bodies**

In a multibody system, a rigid body is an ideal representation of solid body/part of fixed size and shape in which deformation is insignificant or neglected, or in other words, the distance between any two points of a rigid body remains unchanged (irrespective of the external forces acting on it). A rigid body will have six degrees of freedom (DOF) and therefore every additional rigid body in a multibody system adds an additional six DOF to the system.**Deformable Bodies**

Deformable bodies (also called Flex bodies) in multibody systems are those that can be used to model elastic deformation of the bodies of the system. The deformable body connects to its neighboring elements/bodies through interface nodes. The deformable body consists of reduced stiffness and mass matrices, which can be obtained in various ways. Two popular methods for the same are: Craig-Bampton Method and Craig-Chang Method.**Point Mass Bodies**

The point mass body is a reduced version of the six DOF rigid body. It only has three translational DOFs, therefore the point mass body has mass but no inertia properties. The position of a point mass is defined by a center of mass point. By default, the orientation of the point mass is set to be the same as the Global Coordinate System (which never changes during simulation). The purpose of a point mass entity is to add additional representative weight to another body, for example the mass of a driver on a seat.**NLFE Bodies**

NLFE stands for Non Linear Finite Elements. The NLFE implementation in MotionView/MotionSolve is based on Absolute Nodal Coordinate Formulation or ANCF. In this approach, only absolute coordinates and global slopes are used to define the element nodal coordinates without the need for using infinitesimal or finite rotations. In complex multibody simulations, flexible bodies are needed to improve model fidelity. In cases where the deformations and rotations are expected to be large and/or exceed linear assumptions, NLFE becomes a necessity.