# Model Bodies

Bodies are the only modeling elements that explicitly capture mass and inertia effects.

The following three types of bodies are available in MotionSolve:

- Body_Point
- Use this three degree of freedom element when the moment of inertia of the component is negligible, but its mass is significant.
- Body_Rigid
- Use this six degree of freedom element when both mass and inertia are significant, and the deformations are negligible.
- Body_Flexible
- Use this element when the component deformation has a significant effect on
system dynamics or when component stresses are of interest. The deformation
of a flexible body in MotionSolve can be modeled
using the following bodies:
- Linear flexible body
- This method uses linear superposition of modes computed using the Component Mode Synthesis (CMS) method. Several variants of CMS exist, each attempting to accurately capture the deformations and boundary conditions with a minimum number of modes. A CMS-based flexible body contributes degrees of freedom equal to the number of CMS modes in addition to the six degrees of freedom associated with the rigid body motion. This body is able to handle small or linear deformations only.
- Non-Linear Finite Element (NLFE) body
- This method uses the "Absolute Nodal Coordinate Formulation" to obtain a fully non-linear finite element representation of the flexible component. As the name suggests, this body is defined with respect to the global frame and does not have a local part reference frame like the linear flexible body. Each flexible component can be made up of several finite elements that represent flexibility in the component. Similar to traditional finite elements, this flexibility is determined by the geometric and material data specified for the elements. The NLFE body allows you to model geometric non-linearity (large deformations) as well as material non-linearity (hyper-elastic materials like rubber). Current support for the NLFE body is limited to BEAM and CABLE elements only. These elements are useful in modeling long, slender structures.

In addition, it is also possible to define a planar body possessing only three degrees of freedom. This can be specified using Reference_2DCluster and Subsystem_Planar elements.