HEAT AND TEMPERATURE

Heat is a form of energy. Its nature was explained about 150-200 year ago by Rum ford and joule. It is well known that a body becomes hot when heat is added to it. A hot body contains more thermal energy than a cold body. When we rub our hands sometimes, they become warm. In the process of rubbing, one has to do mechanical work and this mechanical energy has produced heat. It means mechanical energy can be converted to heat. While reading on a bicycle, if you apply breaks, the bicycle slows down and the break shoes become hot. A bullet moving with high velocity is brought to rest when it strikes a target; the target becomes warm. In these examples, heat content in bodies increases when they loose mechanical energy. This heat content may also increase due to conversion of chemical, electromagnetic or other forms of energy. All objects require energy to heat up. This energy goes in increasing the internal energy of the body to have a clear idea about the relationship of internal energy with heat, let us consider the composition of matter.  According to the modern science, matter is made of “atoms” and “molecules”, which vibrate about their mean positions in solids and liquids and thus, possess kinetic energy. In gases, molecules move freely until they collide with the wall of the vessels or among themselves. Therefore, they also possess kinetic energy. Molecules in a hot body vibrate more vigorously than molecules in cooler substance. A hot body, when put in contact with a colder body, will loose energy and the transfer of energy takes place from the hot body to cold one. As a result, the hot body becomes cooler due to decrease in kinetic energy of its molecular motion. At the same time molecules in the colder body gain kinetic energy and warm up.

                  HEAT AND TEMPERATURE

 Heat is a form of energy arising from the molecular motion in matter. This energy gives us sensation of hotness or coldness. For example, we fill hot in front of fire. We fill cold when we touch ice. Temperature is a measure of degree of hotness or coldness of a substance. It is also a measure of the average kinetic energy of molecules in a substance as we will see in kinetic theory of gases (chapter-20). Heat and temperature are different physical quantities. Transfer of heat energy always takes place from a hot body to the cold one. In other words heat flows from a body at higher temperature to a body at lower temperature. Thus, temperature gives the direction of heat flow between two bodies when put in thermal contact.