Table of Contents
- Deforming force:
- Elasticity:
- Perfectly elastic body:
- Plasticity:
- Perfectly plastic body:
- Important Point Regarding Elastic Behaviour of Solids
By a rigid body, we generally mean a hard solid object having a definite shape and size. In reality, solid bodies are not perfectly rigid. They can be stretched, compressed and bent. When an external force is applied, a body may get deformed. When the deforming force is removed, some bodies tend to regain their original size and shape while others do not show any such tendency. Let us define few terms to explain this behaviour of bodies.
Deforming force:
If a force is applied on a body which is neither free to move nor free to rotate, the molecules of the body are forced to undergo a change in their relative positions. As a result, the body may undergo a change in length, volume or shape. A force which changes the size or shape of a body is called a deforming force.
Elasticity:
If a body regains its original size and shape after the removal of deforming force, it is said to be elastic body and this property is called elasticity. For example, if we stretch a rubber band and release it, it snaps back to its original length.
Perfectly elastic body:
If a body regains its original size and shape completely and immediately after the removal of deforming force, it is said to be a perfectly elastic body. The nearest approach to a perfectly elastic body is quartz fibre.
Plasticity:
If a body does not regain its original size and shape even after the removal of deforming force, it is said to be a plastic body and this property is called plasticity. For example, if we stretch a piece of chewing-gum and release it, it will not regain its original size and shape.
Perfectly plastic body:
If a body does not show any tendency to regain its original size and shape even after the removal of deforming force, it is said to be a perfectly plastic body. Putty and paraffin wax are nearly perfectly plastic bodies.
Important Point Regarding Elastic Behaviour of Solids
>>No body is perfectly elastic or perfectly plastic.
>>All the bodies found in nature lie between these two limits.
>>When the elastic behaviour of a body decreases, its plastic behaviour increases.