Heat is a form of energy that causes sensation of warmth. We use our sense of touch to decide which object is hotter than the other. The degree of hotness or coldness of a body is called temperature. Temperature is measured by a device called thermometer. Thermometers are classified further on the basis of their uses. Thermometers work on the principle of transfer of heat. Heat is transferred from a hotter object to a colder object. The flow of heat does not take place when the two objects are at same temperature. Heat is transferred between two bodies by conduction, convection and radiation. Heat transfer in solids take place through conduction.The substances are divided into conductors and insulators on the basis of their conduction .

Convection is obesrved in liquids and gases. Convection current always move in upward direction. This propertry of convection current leads to the formation of sea breeze and land breeze.

Radiation is the mode of heat transfer that does not require any medium. The heat from the sun reaches earth through space by the process of radiation. Radiation also makes impact on the kinds of clothes we wear in summer and winter as the dark colours absorb more heat while light colours reflect most of the heat that falls on them.

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