A rigid body does not suffer any distortion under the action of external forces.

Resistant bodies are semi-rigid bodies, normally flexible but under certain loading conditions, act as rigid bodies.

Resistant bodies constitute parts of machines through which requisite motion and forces are transmitted, such as belts, fluids, and springs.

For example:

• A belt is rigid when subjected to tensile force.
• Fluid acts as a rigid body in a hydraulic press during compression.
• Springs behave similarly under specific loading conditions.