Physics Education

Surface Tension - Liquid surface behaves like a stretched membrane. This is because liquid tries to occupy least surface area. This property of liquid is called surface tension (T). Examples Oil & water do not mix with each other. Liquid drops spherical in shape. Small insects can easily walk on the surface of water. Needle can float on the surface of water though density of steel is more than water. Cleaning of clothes by soaps & detergents; which lowers the surface tension of the water. Clinical test for jaundice. some definition from Surface Tension Molecular force - The force which keeps the molecules together is called molecular force.  Cohesive force - It is defined as the force of attraction between molecules of same substances. E.g. force of attraction bet two water molecules. Adhesive force - It is defined as the force of attraction between molecules of different substances. E.g. force of attraction between water molecules & glass molecules. Molecular...

Stress-Strain curve Region OA in the graph is linear. Hook's law is obeyed. Solid behaves like elastic body. Point A is the elastic limit . In region AB, stress & strain are not proportional. But body can  regain its original shape & size when the load is  removed.  Point B is called yield point & corresponding stress is  called yield strength .  When load is removed at point C between region B&D,  body does not regain original dimension. Even stress is zero, strain is not zero in the region BD. P oint C is called set point .  At point C the material is in a permanent set & the deformation is called Plastic deformation. Point D is called ultimate stress . At this point wire becomes thin. Point E represents break point . Where the body physically  breaks. If point D & E are very close, material is said to be brittle . If point D & E are far apart, material is said to be ductile . Ultimate stress ...

Deforming force - An applied external force which changes shape & size of  the   body; known as deforming force. The change of shape & size of the body after application of deforming force is called deformation . Restoring force - When a body is subjected to deforming force a restoring force is developed in the body. This restoring force is equal in magnitude but opposite in direction of deforming force.  Elastic body - If a body regains its original size & shape after removable of deforming force then the body is called elastic body. E.g.   spring, rubber, balloons, Jelly, tennis ball etc. Elasticity - It is defined as a property of a body through which body tends to regain its original size & shape on removal of deforming force. Plastic body - If a body does not regain its original size & shape after removable of deforming force then the body is called plastic body. E.g. wax, putty, toys made of clay etc. Plasticity - It ...