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Reaction[cnum, bnum, point] returns the reaction loads applied by constraint cnum to body bnum, calculated about the specified point. Loads are returned in the format: {force, moment}.
Reaction[cnum, bnum] returns the reaction loads calculated about the local origin of body bnum.
Reaction accepts the
Coordinates option specify whether the resulting load vectors are in Global or body Local coordinates.
Reaction is also a setting for the Type option for Loads.
Type->Reaction causes Loads to return the total kinematic reaction forces applied to a body.

Reaction[cnum, Point[bnum, lpnt]] returns the reaction force applied by constraint cnum to body bnum, calculated about local point lpnt on body bnum.
• The constraint number specification, cnum, can be replaced with any of the specific constraint equation specifications accepted by
• Note that only the reaction moment is a function of the location of point. Reaction forces are not dependent on the point about which they are calculated.
• The default option setting is Coordinates->Global.
Reaction[cnum, symbol] returns the reaction applied by constraint cnum to a particular symbol, in consistent force or moment units. The symbol must be a coordinate or parameter that occurs in the current model's constraint equations.
• The meaning of the quantity returned by Reaction[cnum, symbol] depends on the nature of the occurrence of symbol in the model. For example, if a parameter named len specifies the length of a simple connecting link in the mechanism, the value of Reaction[All, len] corresponds to the tension in the connecting link.
• If symbol occurs in the model in a very complicated and interlinked manner the value returned by Reaction has little physical meaning.
• The alternatives to the Reaction setting for the Type option are Applied and Dynamic, which cause Loads to return external loads or inertial loads, respectively.
• See also: SetLoads.

Further Examples

Load the Modeler2D package and define a simple model.

Here is the total reaction force applied to the link body by all constraints. Note that the numerical value differs if we generate a solution with or without the dynamic loading because the dynamic loading is balanced by the reaction forces.

The total reaction force given by Loads is identical to summing all the independent reaction forces applied by each constraint associated with the link body.

See HelpModel2D.