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101
Meaning of Elasticity and Stress (in Hindi)
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In this lecture you will get the knowledge of property of material which is elasticity and some of the important concepts.

Kartikey Pandey
IIT BHU(B.Tech)| Super 30 Physics Faculty | FOUNDER of New era online coaching. www.youtube.com/neweraonlinecoaching (1,76,000+ Subscribers)

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sir please switch to written notes from next lectures sir, printed se maja nahi aata hai
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1. ELASTICITY

2. The property of a material body by virtue of which it regains its original configuration (i.e. shape and size) when the external deforming force is removed is called elasticity. The property of the material body by virtue of which it does not regain its original configuration when the external force is removed is called plasticity. Deforming force An external force applied to a body which changes its size or shape or both is called deformingforce. Perfectly Elastic body: Abody is said to be perfectly elastic if it completely regains its original form when the deforming force is removed. Since no material can regain completely its original form so the concept of perfectly elastic body is only an ideal concept. A quartz fiber is the nearest approach to the perfectly elastic body

3. perfectly elastic body is only an ideal concept. Aquartz fiber is the nearest approach to the perfectly elastic body Perfectly Plastic body A body is said to be perfectly plastic if it does not regain its original form even slightly when the deforming force is removed. Since every material partially regain its original form on the removal of deforming force, so the concept of perfectly plastic body is also only an ideal concept. Paraffin wax, wet clay are the nearest approach to a perfectly plastic bodies. Cause of Elasticity: In a solid, atoms and molecules are arranged in such a way that each molecule is acted upon by the forces due to the neighboring molecules. These forces are known as intermolecular forces. When no deforming force is applied on the body, each molecule of the solid (i.e. body) is in its equilibrium position and the inter molecular forces between the molecules of the solid are minimum On applying the deforming force on the body, the molecules either come closer or go far apart from each other. As a result of this, the molecules are displaced from their equilibrium position. In other words, intermolecular forces get changed and restoring forces are developed on the molecules. When the deforming force is removed, these restoring forces bring the molecules of the solid to their respective equilibrium positions and hence the solid (or the body) regains its original form

4. Longitudinal or Normal stress When object is one dimensional then force acting per unit area is called longitudinal stress. It is of two types (a) compressive stress (b) tensile stress Tensile stress Compressive strees FIA FIA FIA FIA Examples: (i) Consider a block of solid as shown in figure. Let a force F be applied to the face which has area A. Resolve F into two components = F sin called normal force and F, = F cos called tangential force. F Fsine :. Normal (tensile) stress -

5. Tangential or shear stress It is defined as the restoring force acting per unit area tangential to the surface of the body. Refer to shown in figure above. F Fcose Tangential (shear) stress-A -A The effect of stress is to produce distortion or a change in size, volume and shape (i.e. configuration of the body)

6. Bulk stress When force is acting all along the surface normal to the area, then force acting per unit area is known as pressure. The effect of pressure is to produce volume change. The shape of the body may or may not change depending upon the homogeneity of body

7. STRESS When deforming force is applied on the body then the equal restoring force in opposite direction is developed inside the body. The restoring forces per unit area of the body is called stress. restoring force F stressArea of the body A The unit of stress is N/m2. There are three types of stress