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So that p   w  g  h, then
750 Pa
h   5 , 7 sm.
kg m
1000  10
m 3 s 2

8. MECHANICAL PROPERTIES OF SOLID BODIES

An ideal rigid body does not change its shape under the influence
of forces. Actually, a real solid body undergoes the change in shape or

size when subjected to forces. If the forces applied are not too great, the
body returns to its original condition when they are removed.
When external forces distort a solid object, the changes in size or
shape depend on the physical properties of the material it is made of.

These changes reveal significant and useful information about the
internal forces between the constituent atoms.
Elasticity is that property of a body by which it experiences a

change in shape or volume when a deforming force acts upon it and by
which it returns to its original size or shape when the deforming force is
removed. Materials that do not restore their original shape after being
distorted are said to be inelastic.

The deformation is an alteration of the sizes and the shape of a
solid body. Sometimes, namely for over all strain or compression, the
shape of a body does not change. The reasons of deformations are

external forces, changing of its temperature, etc. In the deformed body
inner elastic forces appear, which balance the external forces.
The deformation is called elastic in the case when it disappears after

the completion of an action of the external forces. Bodies are called
elastic if they can be deformed elastically. Absolutely elastic bodies do
not exist in the nature. But here and after we will consider only

absolutely elastic bodies.
The types of deformations: lengthening, shearing deformation,
bending and torsion .

8.1 Deformations of Lengthening

If the external force F acts on the rod (Fig. 8.1) the deformation of
lengthening takes place and absolute alteration of the length can be
denoted l  x . For elastic distortion the magnitude of deformation is
proportional to the force producing it

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