Class 11th science physics(Mechanical Properties Of Solids)

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What is Elastic Behaviour of Solids?

Elastic Behavior Of Solids – What happens to a rubber band when you stretch it and let go? It deforms but regains its original nature when you stop applying a force. But say, you take an aluminum rod and try to bend it using your arm strength. You somehow do manage to bend it a little and then stop applying force. Does the rod regain its original shape? Of course not. It is referred to as the elastic behavior of solids.

What is Elasticity?

This difference in the behavior of the material is based on their elastic and plastic nature. The rubber band has high elasticity. Elasticity is the ability of a body to resist any permanent changes to it when stress is applied. the body regains its original shape and size when stress application ceases.

What is the Difference Between Elasticity and Plasticity?

All materials have an elastic limit beyond which, if continuous stress is applied, they will start losing their ability to exhibit perfect elastic behavior and start deforming. In contrast, plasticity is the non-reversible deformation of solid materials on the application of forces.
Looking at elasticity in the atomic level, solids are made of atoms (or molecules). They are surrounded by other such atoms which are held in a state of equilibrium by interatomic forces. When an external force is applied these particles are displaced, resulting in the deformation of the solid. When the application of the deforming force is stopped, interatomic forces drive the atoms to regain their state of equilibrium.
The concept of elasticity is an idealization as no material is perfectly elastic. For example, if you use a hair tie to groom yourself, you may have noticed that its size tends to deform after prolonged use. After a point, it may snap as well. This is because the hair tie eventually loses its elastic nature.

Important Points on Elastic Behavior Of Solids

  • An elastic body is one that regains its original shape and size when deforming forces are removed.
  • A plastic body is one that succumbs to deforming forces (however small) and cannot return to its original shape and size.
  • Elasticity is the property of a body to regain its original shape and size when deforming forces are removed. It exhibits an opposition to change.


Today we will look at of of the interesting topics in physics that is bulk modulus. To begin with, bulk modulus is defined as the proportion of volumetric stress related to the volumetric strain of a specified material, while the material deformation is within elastic limit. To put in more simple words, bulk modulus is nothing but a numerical constant that is used to measure and describe the elastic properties of a solid or fluid when pressure is applied on all the surfaces.
Bulk modulus of elasticity is one of the measures of mechanical properties of solids. Other elastic modules include young's modulus  and Shear modulus. In any case, the bulk elastic properties of a material is used to determine how much it will compress under a given amount of external pressure. Here it is important to find and note the ratio of the change in pressure to the fractional volume compression.
The value is denoted with a symbol of K and it has the dimension of force per unit area. It is expressed in the units of per square inch (psi) in the English system and newtons per square meter (N/m2) in the metric system.

Bulk Modulus Of Elasticity Formula

It is given by the ratio of pressure applied to the corresponding relative decrease in volume of the material. The relation is given below.
B = ΔP /(ΔV/V)
Where:
B: Bulk modulus
ΔP: change of the pressure or force applied per unit area on the material
ΔV: change of the volume of the material due to the compression
V: Initial volume of the material in the units of in the English system and N/m2 in the metric system.

Uses

Bulk modulus is used to measure how incompressible a solid is. Besides, the more the value of K for a material, higher is its nature to be incompressible. For example, the value of K for steel is 1.6×1011N/m2and the value of K for glass is 4×1010N/m2. Here, K for steel is more than three times the value of K for glass. This implies that glass is more compressible than steel.
Now, a quick exercise for you. Try finding the value for diamond and comparing it with the value of steel and glass.
Consider this situation. You go deep sea diving into the Mariana Trenches. This is the following information you have in hand.
Bulk Modulus of Bone = 1.5×1010N/m2
Atmospheric Pressure = 1.01×105N/m2
Pressure at deep point = 1.09×108N/m2

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