Reaction Force

Definition - What does Reaction Force mean?

A reaction force is a force that acts in the opposite direction to an action force. Friction is the reaction force resulting from surface interaction and adhesion during sliding. Reaction forces and reaction moment are usually the result of the actions of applied forces.

When reaction forces exceed action forces, structure failure can occur and may lead to fracture as well as corrosion.

Corrosionpedia explains Reaction Force

A reaction force is the force applied to a structure when it rests against something. In analyzing a beam structure, it involves calculating what the reaction forces are at the supports due to the forces acting on the beam. A free body diagram of the entire beam can be used to determine the reaction forces.

The beam has vertical and horizontal reaction forces as well as a reaction moment. The horizontal reaction force is zero as long as there are no horizontal applied forces. A cantilever beam with a single support has a reaction force and a reaction moment. The reaction force equals the sum of the applied forces on the beam. If the beam sits on a roller that allows the beam to move freely horizontally, its support has only a vertical reaction force.

When put under compression (or any other type of stress), every material suffers some deformation, even if imperceptible, that causes the average relative positions of its atoms and molecules to change. The deformation may be permanent, or may be reversed when the compression forces disappear. In the latter case, the deformation gives rise to reaction forces that oppose the compression forces, and may eventually balance them. Liquids and gases cannot bear steady uniaxial or biaxial compression — they deform promptly and permanently and do not offer any permanent reaction force.

Reaction forces can cause corrosion, for example, bearings' reaction forces increases with decreasing the bearing clearances from 350mm to 150mm due to increased stiffness of the system. The reaction forces are correlated to the compression of the different core of bearing materials. It can cause damages of cores and delaminations of face sheets.

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