UNIT 1

STATE OF MATTER, WORK AND MOTION

STATES OR PHASES OF MATTER. In its fundamental connotation , the term state refers to the condition of a substance ,as its state of aggregation ,which may be solid, liquid or gaseous- compact or dispersed .

A solid is a state of matter in which the substance possesses both definite volume and definite shape. Solids possess elasticity of shape due to the binding forces between their molecules ,which offer opposition to any change in the shape of the body .

A liquid is a state of matter in which the substance has no definite shape but takes the shape of the vessel in which it is plated. The binding forces between molecules ,are much less than when a substance is a solid. Liquids have no hardness or rigidity and are characterized by free flow. They also possess a free boundary surface .

A gas is a state of matter in which the molecules move freely and consequently the entire mass tends to expand indefinitely , occupying the total volume of any vessel into which it is placed. Gasses have no definite shape or volume. Unlike liquids gases have no free surface .

Work. In the strict physical sense , work is performed only when a force is exerted on a body in such a way that both the body and the force move through a distance .The amount of work done during motion from point a to point b can be expressed by :

W=∫a

b

FcosQds

Where F is the total force exerted, and Q is the angle between the direction of F and the direction of the elemental displacement ds .In the MKS (metric) system ,the unit of work is the Newton-meter or joule and in the English system ,the foot-pound.

MOTION. Motion is a progressive change of position of a body. The motion of a body may be one of pure translation or pure rotation. The general motion of a rigid body, however , is a combination of translation and rotation . Translation is a motion is which all points of a system have identical displacements . If each point moves on straight line , the translations rectilinear ,if on curve ,it is curvilinear .Rotation is a motion in which all particles of a body move in circles about common axis with a common angular velocity . This motion may be either free or constrained , as illustrated , respectively by the earth turning on its axis, and by a flywheel or a pendulum .