# Bodies

Model body geometries, inertias, colors, and frames

Model a body using Solid and Rigid Transform blocks. The Solid blocks provide the geometries, inertias, and colors of the solid sections of the body. The Rigid Transform blocks specify the spatial relationships—the relative positions and orientations—of those solid sections. A solid section can have a simple shape such as `Sphere` or `Brick`, a more sophisticated shape such as `General Extrusion` and `Revolution`, or an arbitrarily detailed shape imported from a STEP or STL file.

## Simscape Blocks

 Graphic Marker with graphic properties Inertia Mass element with fixed inertial properties Solid Solid element with geometry, inertia, and color General Variable Mass Mass element with variable inertial properties Variable Brick Solid Solid brick with variable mass and size Variable Cylindrical Solid Solid cylinder with variable mass and size Variable Spherical Solid Solid sphere with variable mass and size
 Spline Cubic interpolating plane curve or space curve
 Reference Frame Non-inertial reference frame Rigid Transform Fixed spatial relationship between frames

## Functions

 `smnew` Open Simscape Multibody model template and block library `sm_lib` Open the Simscape Multibody block library

## Topics

### Bodies

Bodies Workflow

Bodies, the core constituents of a multibody model, comprise body elements, each in turn comprising frames and attributes. Modeling a body is more than adding a block to a model. Here are some general steps to keep in mind when modeling one.

Modeling Bodies

Bodies are representations that you create of physical parts—gears, pistons, levers—for later assembly into multibody systems, a piston engine serving as an example. Here is an introduction to bodies as well as the blocks and tools commonly used to represent one in a model.

Compounding Body Elements

A typical body is a rigid collection of solids and other body elements. In this sense, it is a compound unit. Learn how you can use compounding to create complex geometries and inertias from simpler ones.

### Geometry

Representing Solid Geometry

Geometry is a key attribute of solids and of the bodies they comprise. You can specify the shape and size of a solid using the Solid block. Here is an introduction to the types of shapes that you can specify (or import) using this block.

Modeling Extrusions and Revolutions

`General Extrusion` and `Revolution` are the most versatile of the preset solid shapes. Their cross-sections are custom and set by coordinate matrices that you specify. Here is an introduction to both the shapes and the cross-sections that define them.

### Inertia

Representing Solid Inertia

Inertia quantifies the resistance of a body to changes in motion and is among the most important attributes in a model. Here is an introduction to the types of inertias that you can represent in a model as well as the blocks and parameterizations that you can use to do so.

Specifying Custom Inertias

"Inertia" is a general term often used to mean mass, center of mass, the moments of inertia, and the products of inertia. Learn more about these inertia parameters and how they are defined in the Simscape Multibody environment.

Specifying Variable Inertias

Not all inertias remain constant during simulation. Some can vary and it is often their changing parameters that most matter in a model. Learn more about variable inertias and how you can specify their parameters in a model.

### Frames

Working with Frames

Frames are axis triads that encode the position and orientation of body elements in a body. Learn about frames as a means to connect body elements and about rigid transforms as a means to offset those elements.

Creating Connection Frames

Often, you must create new frames for use in joint and constraint connections. Learn how you can create such frames and how joints and constraints affect their placements in a body.

Creating Custom Solid Frames

All solids have a local reference frame but you can create other, custom, frames, for connection in a model. Learn how you can perform this task using the frame creation panel of the Solid block.

### Visualization

Manipulate the Color of a Solid

Color helps to differentiate bodies and contributes to the effectiveness of a multibody visualization. Learn about the color parameters that you can specify and their impact on the appearance of your bodies.

Visualize a Model and Its Components

Visualization is not only a central part of a multibody simulation, it is an essential tool in modeling bodies and verifying their shapes, sizes, frame placements, and colors. Here is an overview of the visualization utilities available in the Simscape Multibody environment and the roles they play in your modeling workflow.