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the capability of a body or structure to resist deformation; a physicogeometric characteristic of the cross section of a structural element. In the case of simple deformations within the limits of Hooke’s law, rigidity is determined numerically as the product of the modulus of elasticity E (on elongation-contraction and on flexure) or G (on shear and torsion) and some geometric characteristic of the element cross section:EF on elongation-compression, El on flexure, GF on shear, and so on, where F is the cross section area, and I is the axial moment of inertia. The concept of rigidity is being widely used in the solution of problems concerning the strength of materials.
in physiology, a functional state of the skeletal muscles, characterized by a marked increase in their tone and in their resistance to deformation. Muscle rigidity results from changes in the character of the neural influences that the central and peripheral nervous systems continuously exert to the muscles. An example of rigidity is decerebrate rigidity.
In man, injuries and disturbances of the central nervous system and pathological irritation of the peripheral nerves give rise to various manifestations of muscle rigidity. Thus, poisoning by certain toxins, diseases of the nervous system, and hypnosis may cause a state of plastic tone, characterized by a waxlike condition of the muscles. In this state the extremities may easily be placed in any position and can remain thus, unchanged, for a prolonged period. Plastic tone characterizes a state of the nervous system called catalepsy, or plastic rigidity.
ii. A property of a gyroscope by which its axis will remain in a fixed direction in space unless the rotor is acted upon by an external torque.