Mechanical Properties of Solids | Elasticity

Mechanical Properties of Solids-

 Mechanical properties of solids are those properties of solids which define its solidity. OR Mechanical properties of solids are those physical properties that a solid exhibits upon the application of forces.

Examples of Mechanical Properties of Solids are-

• Hardness
• Tensile strength
• Resistance to deformation
• Elasticity
• Plasticity
• Ductility and many more…

Rigid Bodies-

 The materials having a definite shape and size are called as rigid bodies.

• A perfectly rigid body does not lose its shape or size under the influence of any external force.
• The distance between its molecules always remains the same under the action of any external force.
• There is no body which is perfectly rigid.
• The nearest approach to a perfectly rigid body are diamond, carborundum etc.

Deforming Force-

 An external force which changes the configuration  (shape or size) of a body is called as a deforming force.

• When an external force is applied on a body which is neither free to move nor free to rotate, the molecules of the body are forced to change their relative positions.
• Due to this change, the body may suffer a change in its shape or size.
• Such a force which changes the shape or size of a body is called as a deforming force.

Restoring Force-

 An internal force which helps to body to regain its original configuration after the deforming force acting on it is removed is called as restoring force.

• When a deforming force is applied on a body, a force is developed within the body on account of relative molecular displacement.
• This force helps the body to regain its original configuration (shape and size) and is called as restoring force.
• This restoring force accounts for the elastic behavior of solids.

Elasticity-

 The property of a solid body by virtue of which it tends of regain its original configuration (shape and size) when the deforming force acting on it is removed is called as elasticity.

For example-

If we stretch a rubber band and release it, it snaps back to its original length. So, it is elastic.

Types of Elastic Bodies-

 Those bodies which possess the property of elasticity are called as elastic bodies.

Based on the degree of elasticity, the elastic bodies can be categorized under the following three types-

1. Perfectly Elastic Bodies
2. Partially Elastic Bodies
3. Perfectly Plastic Bodies

1. Perfectly Elastic Bodies-

 A body is said to be perfectly elastic if it completely regains its original configuration (shape and size) after the deforming force acting on it is removed.

• Since no body can completely regain its original configuration, so the concept of perfectly elastic body is only an ideal concept.
• The nearest approach to a perfectly elastic body are quartz fiber and phosphor bronze.

2. Partially Elastic Bodies-

 A body is said to be partially elastic if it regains its original configuration (shape and size) partially (not completely) after the deforming force acting on it is removed.

• All the materials regain their original configuration partially on the removal of deforming force.

3. Perfectly Plastic Bodies-

 A body is said to be perfectly plastic if it does not regain its original configuration (shape and size) even slightly after the deforming force acting on it is removed.

• Since every material partially regain its original configuration on the removal of deforming force, so the concept of perfectly plastic body is only an ideal concept.
• The nearest approach to a perfectly plastic body are paraffin wax, mud and putty.

Plasticity-

 The property of a solid body by virtue of which it does not regain its original configuration (shape and size) after the deforming force acting on it is removed is called as plasticity.

When the elastic behavior of a body decreases, its plastic behavior increases.