Every matter in the universe is composed of tiny particles called molecules. They attract each other with some attractive force. There exists an intermolecular force of attraction between molecules. Based on the force of attraction between the molecules, matter are classified into five categories. They are solid, liquid, gas, plasma, and Bose-Einstein. Solids are matter in which the distance between the molecules is very small and they are tightly bound to each other.
When a force is applied to a body it gets deformed. If the body regains its original shape after the removal of force from the body then the force is called elastic force. As it deforms the dimension of the body it is called a deforming force. This phenomenon of the body is called elasticity. When s rubber is stretched by force, the length and thickness of the rubber change. After removing the force it gets to its original size. This property is called elasticity.
Each atom or molecule in solids is connected with the neighboring atoms by interatomic forces and stays in an equilibrium position. When the deforming force is applied to the solid the interatomic distance between the atoms changes because the atoms dislocate from the equilibrium position. After the removal of the deforming force, the interatomic force tends to attract the atoms to their original position. Thus the solid returns to its original position. The applied force is the stress applied to the solid. Due to the stress applied to the body, there is a change in the dimensions of the body. This change is called the strain.
Stress
The force applied to the body which changes the dimensions of the body is called stress.
$$\mathrm{force=\frac{stress}{strain}}$$
Unit of stress is $\mathrm{Nm^{-2}}$
Strain
When stress is applied to a body it gets deformed. The ratio between the change in dimension to its original dimension is known as strain.
$$\mathrm{stress=\frac{change\:in\:dimension}{original\:dimension}}$$
It has no unit.
The mechanical properties of solids are characterized by the strength and resistance of the solid to the deforming force. It is the ability of the solid to remain unchanged due to the stress applied to it. It also has resistance to change. If the resistance of the body to the deforming force is less, then it gets deformed easily. Some of the mechanical properties are given below.
Elasticity − When a force is applied to a body, the shape of the body changes. If it regains its shape after the removal of force it is called elasticity.
Plasticity − If the body cannot regain its original shape after the removal of deforming force, it is called plasticity.
Ductility − It is the ability of the solid material to stretch into a thin sheet, wire, or plate is called ductility.
Strength − If the solid material sustains the deforming force without fail, that ability is the strength of the solid material.
As the intermolecular distance between the molecules of the solid material is small the force between them is very strong.
The molecules in the solid materials are placed very close to each other. As the distance between them is small, solid materials are incompressible.
Due to the small separation of the distance they are hard and rigid.
Solid materials have definite mass and volume and they are fixed.
Molecules in solid are not free to move as they are tightly bound. So they can only oscillate about their mean position.
Solid can pass current through them.
Chemical changes make changes in the composition of the matter.
The elastic behavior of solid materials is used in many fields. Some of these applications are given below.
Carrying heavy loads is done with strong materials. The Load carried by cranes and lifts is very high. So the ropes and cables used for suspensions should be made of strong material. So materials having higher young’s modulus are used for the ropes and cables.
Knowing the strength of the solid materials is possible by the elastic behavior of the material. By the knowledge of this property, materials that best suit the construction of pillars, and columns for building are selected.
Knowledge about the elastic behavior of the materials is very much important in engineering.
Principle of elasticity is also useful in measuring the height of mountains.
Bridges should not get deformed due to heavy traffic or hurricanes. That is done by knowing the elastic property of solids.
The metallic parts of the machines get deformed if the force exceeds the elastic limit. Proper choosing of material is done by this property.
Some properties that affect the properties of solids. They are given below.
Even Though the elastic limit of the solid material is not crossed if the stress is applied multiple times it may affect the tensile strength of the material. So the stress factor of the material should be lower than the tensile strength of the material.
The elastic property of the material is inversely proportional to temperature. That is, elasticity is high at low temperature and low at high temperature.
Elasticity depends on the nature of the material. If it is a single crystal then it has high elasticity. If it is a polycrystal then it has low elasticity.
To improve the material’s softness the material is heated to a very high temperature and tends to cool down slowly. This process is called annealing. This may produce grains in the material which reduces its elasticity.
Depending upon the impurity added to the material there is a gain or loss of elasticity in the material.
Matters are classified into five. Among these, the properties of solids are discussed in this article. Elasticity and the elastic behavior of solid materials are discussed above. The mechanical, physical, and chemical properties of solids were discussed in this article in detail. In addition to that, the applications of elastic behavior of solids and the factor that affects the properties of solids are also discussed.
Q1. What is an elastic limit?
Ans. If stress is applied to a body it gets deformed. After the removal of that stress, it returns to its original position. There is maximum stress before which the body is able to regain its dimension known as the elastic limit. Beyond this limit, the body cannot regain its original dimensions.
Q2. Define Hooke's law.
Ans. Inside the elastic limit, the strain formed in the material is directly proportional to the stress applied.
$$\mathrm{stress\propto strain}$$
Which is known as Hooke’s law.
Q3. What is the modulus of elasticity?
Ans. Modulus of elasticity gives the relation between stress and strain. The ratio between the stress applied to the material and the strain formed due to the applied stress is constant. This constant is called the modulus of elasticity.
$$\mathrm{\frac{stress}{strain}=K}$$
There are three types of modulus of elasticity. They are Young’s modulus, Rigidity modulus, and bulk modulus.
Q4. Differentiate elasticity and plasticity
Ans.
| Elasticity | Plasticity |
|---|---|
| It regains its shape after the removal of the force applied. | It is deformed after the removal of the force applied. |
| Small amount of force needed. | It needs a greater amount of force. |
| It obeys Hooke’s law inside the elastic limit. | It does not obey Hooke’s law. |
| Stress-strain behavior is linear. | Stress-strain behavior is non-linear. |
Q5. How does the modulus of elasticity differ from the modulus of rigidity?
Ans. The modulus of elasticity explains the deformation of the material when the applied force is in the perpendicular direction while the modulus of rigidity explains the deformation of the material when the applied force is in a parallel direction.
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