The figures given in the tables should be taken as indications rather than fixed values, and as applicable to a large number collectively and not to individual pieces.
FUNDAMENTAL CONSIDERATIONS AND DEFINITIONS Study of the mechanical properties of a material is concerned mostly with its behavior in relation to stresses and strains, and the factors affecting this behavior.

A ~stress~ is a distributed force and may be defined as the mutual action (1) of one body upon another, or (2) of one part of a body upon another part.

In the first case the stress is _external_; in the other _internal_.

The same stress may be internal from one point of view and external from another.

An external force is always balanced by the internal stresses when the body is in equilibrium.
If no external forces act upon a body its particles assume certain relative positions, and it has what is called its _natural shape and size_.