INTRODUCTION :
Heat is a form of energy. We know that energy means capacity to do work. So we can say, heat, being a form of energy, can do work. For example, when pressure cooker is heated, steam is formed within the cooker and this steam can lift the lid of the                pressure cooker. In this chapter we shall study about the meaning of hot and cold and how things are heated or cooled.

TEMPERATURE - DEGREE OF HOTNESS  ORCOLDNESS :
When we touch an ice cube, we say it is cold. Similarly when we touch a cup of tea, we say it is hot. Here we compare the hotness or coldness of an object with that of our hand. But sensing the hotness or coldness by touching is not always true. “The               degree of hotness or coldness of a substance is called its temperature.” When two objects at different temperatures are kept in contact, heat flows from hotter object (high temperature) to colder object (low temperature). So direction of heat flow is governed      by the temperatures of the objects in contact. It should be kept in mind that exchange of heat continues so long as the temperatures of the two objects remains unequal. Heat flow stops as soon as temperatures become equal which is known as thermal              equilibrium.

Differences Between Heat and Temperature :