Axioms of Statics

The axioms of statics are the starting principles for studying the equilibrium of a rigid body.

1. Two-force equilibrium. Two forces acting on a rigid body balance if and only if they have equal magnitudes, act along the same straight line, and point in opposite directions.
2. Addition or removal of a balanced force system. The mechanical effect of a force system on a rigid body is unchanged when a balanced force system is added or removed.
3. Parallelogram law of forces. Two forces applied at the same point have a resultant applied at that point and equal to their vector sum: the diagonal of the parallelogram constructed on the two force vectors.
4. Action and reaction. The interaction forces between two bodies are equal in magnitude, opposite in direction, and collinear. They act on different bodies and therefore do not form a balanced force system on either body alone.
5. Principle of rigidification. A deformable body in equilibrium remains in equilibrium if it is regarded as rigid in its current configuration.