Rigid body where body rotation and inertia tensor is neglected (6 potential states)


This information is part of the Modelica Standard Library maintained by the Modelica Association.

Rigid body where the inertia tensor is neglected. This body is solely defined by its mass. By default, this component is visualized by a sphere that has its center at frame_a. Note, that the animation may be switched off via parameter animation = false.

Every PointMass has potential states. If possible a tool will select the states of joints and not the states of PointMass because this is usually the most efficient choice. In this case the position and velocity of frame_a of the body will be computed by the component that is connected to frame_a. However, if a PointMass is moving freely in space, variables of the PointMass have to be used as states. The potential states are: The position vector frame_a.r_0 from the origin of the world frame to the origin of frame_a of the body, resolved in the world frame and the absolute velocity v_0 of the origin of frame_a, resolved in the world frame (= der(frame_a.r_0)).

Whether or not variables of the body are used as states is usually automatically selected by the Modelica translator. If parameter enforceStates is set to true in the "Advanced" menu, then PointMass variables frame_a.r_0 and der(frame_a.r_0) are forced to be used as states.

Parameters (3)


Value: true

Type: Boolean

Description: = true, if animation shall be enabled (show sphere)



Type: Mass (kg)

Description: Mass of mass point


Value: StateSelect.avoid

Type: StateSelect

Description: Priority to use frame_a.r_0, v_0 (= der(frame_a.r_0)) as states

Inputs (3)


Default Value: world.defaultBodyDiameter

Type: Diameter (m)

Description: Diameter of sphere


Default Value: Modelica.Mechanics.MultiBody.Types.Defaults.BodyColor

Type: Color

Description: Color of sphere


Default Value: world.defaultSpecularCoefficient

Type: SpecularCoefficient

Description: Reflection of ambient light (= 0: light is completely absorbed)

Connectors (1)


Type: Frame_a

Description: Coordinate system fixed at center of mass point

Components (2)


Type: World


Type: Shape

Used in Examples (1)



Two point masses in a point gravity field (rotation of bodies is neglected)

Extended by (1)



Point mass used at all places of this example