Before the equilibrium of rigid bodies can be investigated, the supports that hold them in place, or hold them to other objects, must be first analyzed.
Supports that are commonly found in statics can be represented by stylized models called support conventions. An actual support may be a close approximation of a model. The forces and moments exerted on a rigid body by its supports are called reactions. These forces and moments are reacting to external loads that are applied to the rigid body.
In general, if a support prevents translation in a given direction, then the support exerts a force in that direction. If rotation is prevented,
then the support exerts a couple, or moment, in the direction of the rotation.
Supports can be broken down into two categories: 2-D supports and 3-D supports. The table to the left shows common 2-D support conventions.
To better understand the relationship between support conventions and support reactions, detailed explanation of three of the more commonly used support conventions are presented below. They are the pin support, the roller support, and the fixed support.