Section 10.1 Heat
Standing out in a scorching summer day we feel hot and touching an iron bar in the morning of a severing winter day, we feel cold. The sensation of hotness and coldness can be experienced by the increase or decrease of a certain kind of energy which we call heat. Heat is a form of energy that can transfer from one location to another because of the temperature difference between them. A quantitative measure of the sensation of hotness or coldness is given by temperature. Therefore, temperature is the degree of hotness or coldness of a body. Heat energy is produced at the expense of mechanical energy and vice versa. For example, rubbing palms vigorously makes palm warmer. An infinite amount of heat can be extracted from a substance by continually doing mechanical work on it just as heat is obtained from water in Joule’s experiment. Work and heat both transfer the energy from one system to another but temperature plays no role in transfer of energy due to work. Objects can store heat (or thermal energy) because the atoms and molecules of the objects are jostling around and bumping into one another. This type of thermal energy is called internal kinetic energy of the materials. The energy also arise in molecules due to intermolecular attractions. This type of energy is called internal potential energy. During phase change of a material heat is stored in the form of internal potential energy. For example, heating of ice melts it without any rise of temperature. This energy is used in driving the molecules of ice away from each other against their molecular attraction. While internal energy refers to the total energy of all the molecules within the object, heat is the amount of energy flowing from one body to another spontaneously due to their temperature difference. Heat is energy in transit but not a property of the system.
To measure how hot or cold something is, we use an instrument called a thermometer. Hence, the thermometer is a device used to measure temperature. The definition of temperature is not very straight forward to explain but the degree of hotness or coldness of a body would suffice the definition for now. We will discuss more in defining the temperature in thermodynamics chapter.
