Answer:

3.To begin, forces always act in pairs and always act in opposite directions. When you push on an object, the object pushes back with an equal force. ... This is the action force. The table exerts an equal upward force on the books. This is the reaction force.

4.A reaction force is a force that acts in the opposite direction to an action force. ... 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.