MECHANICAL PROPERTIES OF SOLIDS L 1.pptx

class 11 physics

1. MECHANICAL PROPERTIES OF SOLIDS

2. Elastic and Plastic Behaviour of Solids – Deforming Force – A force which changes the size or shape of a body is called deforming force. Elasticity – If a body regains its original shape and size after the removal of deforming force, it is said to be elastic body and the property is called elasticity. Perfectly Elastic Body – If a body regains its original shape and size completely and immediately after the removal of the deforming force, it is said to be perfectly plastic body. Example – Quartz.

3. Plasticity – If a body do not regain its original shape and size even after the removal of the deforming force, it is said to be a plastic body and this property is called plasticity. Example – Chewing gum Perfectly Plastic Body – If a body does not show any tendency to regain its original shape and size even after the removal of deforming force, it is said to be a perfectly plastic bodies.

4. Elastic Behaviour in terms of Interatomic Forces The atoms in a solid are held together by interatomic forces.

5. Elastic behaviour of solids on the basis of mechanical spring ball model of a solid The atoms in a solid may be regarded as mass point or small bulbs connected in 3 D space through springs. The springs represent the interatmoic forces.

6. Stress – The internal restoring force set up per unit area of cross – section of the deformed body is called stress. Types of Stress Tensile Stress Compressional Stress Hydrostatic Stress Tangential or Shearing Stress

7. Tensile Stress – It is the restoring force set up per unit cross sectional area of a body when the length of the body increases in the direction of the deforming force. It is also called Longitudinal stress. Compressional Stress - It is the restoring force set up per unit cross sectional area of a body when the length of the body decreases in the direction of the deforming force. It is also called Longitudinal stress. Hydrostatic Stress – If a body is subjected to a uniform force from all sides, then the corresponding stress is c alled hydrostatic stress. Tangential or Shearing Stress – Whe n a deforming force acts tangentially to the surface of a body. It produces a change in the shape of the body. The tangential force applied per unit area is equal to the tangential stress.