8th Class Science Combustion and Flame Heat

       Heat

Heat is the transfer of energy from one part of a substance to another, or from one body to another by virtue of a difference in temperature. Heat is energy in transit; it always flows from a substance at a higher temperature to the substance at a lower temperature, raising the temperature of the latter and lowering that of the former substance, provided the volume of the bodies remains constant.

              Temperature

The sensation of warmth or coldness of a substance on contact is determined by the property known as temperature. Although it is easy to compare the relative temperatures of two substances by the sense of touch, it is impossible to evaluate the absolute magnitude of the temperatures by subjective reactions. Adding heat to a substance, however, not only raises its temperature, causing it to impart a more acute sensation of warmth, but also produces alterations in several physical properties, which may be measured with precision. As the temperature varies, a substance expands or contracts, its electrical resistivity changes, and in the gaseous form, it exerts varying pressure. The variation in a standard property usually serves as a basis for an accurate numerical temperature scale..