Mechanical Properties of Solids
• Inter molecular Force
In a solid, atoms and molecules are arranged in such a way that each molecule is acted
upon by the forces due to the neighbouring molecules. These forces are known as inter
molecular forces.
• Elasticity
The property of the body to regain its original configuration (length, volume or shape)
when the deforming forces are removed, is called elasticity.
• The change in the shape or size of a body when external forces act on it is determined
by the forces between its atoms or molecules. These short range atomic forces are
called elastic forces.
• Perfectly elastic body
A body which regains its original configuration immediately and completely after the
removal of deforming force from it, is called perfectly elastic body. Quartz and phospher
bronze are the examples of nearly perfectly elastic bodies.
• Plasticity
The inability of a body to return to its original size and shape even on removal of the
deforming force is called plasticity and such a body is called a plastic body.
• Stress
Stress is defined as the ratio of the internal force F, produced when the substance is
deformed, to the area A over which this force acts. In equilibrium, this force is equal in
magnitude to the externally applied force. In other words,
• Stress is of two types:
(i) Normal stress: It is defined as the restoring force per unit area perpendicular to the
surface of the body. Normal stress is of two types: tensile stress and compressive
stress.
(ii) Tangential stress: When the elastic restoring force or deforming force acts parallel to
the surface area, the stress is called tangential stress.
• Strain
It is defined as the ratio of the change in size or shape to the original size or shape. It
has no dimensions, it is just a number.
Strain is of three types:
(i) Longitudinal strain: If the deforming force produces a change in length alone, the
strain produced in the body is called longitudinal strain or tensile strain. It is given as:
, (ii) Volumetric strain: If the deforming force produces a change in volume alone, the
strain produced in the body is called volumetric strain. It is given as:
(iii) Shear strain: The angle tilt caused in the body due to tangential stress expressed is
called shear strain. It is given as:
• The maximum stress to which the body can regain its original status on the removal of
the deforming force is called elastic limit.
• Hooke’s Law
Hooke’s law states that, within elastic limits, the ratio of stress to the corresponding
strain produced is a constant. This constant is called the modulus of elasticity. Thus
• Stress Strain Curve
Stress strain curves are useful to understand the tensile strength of a given material.
The given figure shows a stress-strain curve of a given metal.
• Inter molecular Force
In a solid, atoms and molecules are arranged in such a way that each molecule is acted
upon by the forces due to the neighbouring molecules. These forces are known as inter
molecular forces.
• Elasticity
The property of the body to regain its original configuration (length, volume or shape)
when the deforming forces are removed, is called elasticity.
• The change in the shape or size of a body when external forces act on it is determined
by the forces between its atoms or molecules. These short range atomic forces are
called elastic forces.
• Perfectly elastic body
A body which regains its original configuration immediately and completely after the
removal of deforming force from it, is called perfectly elastic body. Quartz and phospher
bronze are the examples of nearly perfectly elastic bodies.
• Plasticity
The inability of a body to return to its original size and shape even on removal of the
deforming force is called plasticity and such a body is called a plastic body.
• Stress
Stress is defined as the ratio of the internal force F, produced when the substance is
deformed, to the area A over which this force acts. In equilibrium, this force is equal in
magnitude to the externally applied force. In other words,
• Stress is of two types:
(i) Normal stress: It is defined as the restoring force per unit area perpendicular to the
surface of the body. Normal stress is of two types: tensile stress and compressive
stress.
(ii) Tangential stress: When the elastic restoring force or deforming force acts parallel to
the surface area, the stress is called tangential stress.
• Strain
It is defined as the ratio of the change in size or shape to the original size or shape. It
has no dimensions, it is just a number.
Strain is of three types:
(i) Longitudinal strain: If the deforming force produces a change in length alone, the
strain produced in the body is called longitudinal strain or tensile strain. It is given as:
, (ii) Volumetric strain: If the deforming force produces a change in volume alone, the
strain produced in the body is called volumetric strain. It is given as:
(iii) Shear strain: The angle tilt caused in the body due to tangential stress expressed is
called shear strain. It is given as:
• The maximum stress to which the body can regain its original status on the removal of
the deforming force is called elastic limit.
• Hooke’s Law
Hooke’s law states that, within elastic limits, the ratio of stress to the corresponding
strain produced is a constant. This constant is called the modulus of elasticity. Thus
• Stress Strain Curve
Stress strain curves are useful to understand the tensile strength of a given material.
The given figure shows a stress-strain curve of a given metal.
