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The deformation  is often called deformation per unit of
length and - relative shift.
Totality of deformations per unit of length  in different
directions and angular deformations  in different planes that pass
through the considered point characterizes deformed state at the
point.
Knowing the deformation of the body in all its points and fixing
conditions, we can determine the displacement of any point of the
body, that is, show the position of (coordinates) after applying the
load.

1.4 Limitations and principles adopted in strength of
materials

1.4.1 Smallness of deformations (the principle of
original dimensions)

The ability to use solids as structural materials is based on the
fact that the deformations of such bodies are small in comparison
with their sizes. Therefore, they are limited by the examination of
only small deformations. This limitation allows:
- in the equations of equilibrium do not take into account
changes in the location of external forces that occur as a
result of the deformation of a body;
- for materials with nonlinear deformation law adopt a linear
relationship between load and deformation.

1.4.2 The principle of superposition

When the deformations in the elastic system are small and
linearly related with the forces, the superposition principle is

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