- Physics Properties of Matter – 01
- PROPERTIES OF MATTERS
- HOOKE’S LAW
Physics Properties of Matter – 01
According TO KINETIC THEORY OF MATTER: (i). Molecules Are In The State Of Continuous Motion In All Possible Directions And Hence They Possess Kinetic Energy Which Increases With The Gain Of Heat Energy Or Rise In Temperature, (Ii). The Molecules Always Attract Each Other, (Iii). The Force Of Attraction Between The Molecules Decreases With The Increase In Intermolecular Spaces
The molecules always attract each other. The force of attraction between the similar kinds of Molecules Is Called FORCE OF COHESION whereas the force of attraction between different kinds of molecules is called force of adhesion.
- In case of solids, the intermolecular space being very small, so intermolecular forces are very large and hence solids have definite size and shape.
However, if you apply force to a lump of putty or mud, they have no gross tendency to regain their previous shape, and they get permanently deformed. Such substances are called plastic and THIS PROPERTY IS CALLED PLASTICITY. Putty and mud are close to ideal plastics. When a force is applied on body, it is deformed to a small or large extent depending upon the nature of the material of the body and the magnitude of the deforming force. The deformation may not be noticeable visually in many materials but it is there. When a body is subjected to a deforming force, a restoring force is developed in the body. This restoring force is equal in magnitude but opposite in direction to the applied force. The RESTORING FORCE PER UNIT AREA IS KNOWN AS STRESS. If F is the force applied and A is the area of cross section of the body, Magnitude of the stress = F/A. THE SI UNIT OF STRESS IS N M−2 OR PASCAL (PA). Stress is the restoring force per unit area and strain is the fractional change in dimension.
Robert Hooke, An English Physicist (1635 – 1703 A.D) performed experiments on springs and found that the elongation (change in the length) produced in a body is proportional to the applied force or load. In 1676, he presented his law of elasticity, now CALLED HOOKE’S LAW. For small deformations the stress and strain are proportional to each other. This is known as Hooke’s law. Thus, stress” strain or stress = k X strain, where k is the proportionality constant and is known as modulus of elasticity. The basic property of a fluid is that it can flow. The fluid does not have any resistance to change of its shape. Thus, the shape of a fluid is governed by the shape of its container. A liquid is incompressible and has a free surface of its own. A gas is compressible and it expands to occupy all the space available to it.