# Heat and Temperature

## What is heat?What is temperature?

Heat is a kind of energy. We have seen that energy can do work. By applying force it is possible to displace a body in the direction of the force, for example, heat is produced by burning fuel oil in a train or a car and this produced energy creates motion in the train or car. So this new form of energy is called heat energy like electricity or kinetic energy.

It is interesting that if we could see on the molecular level i.e, looking at any substance if we see its molecules, we should call it "kinetic energy" instead of the "heat energy".

We may regard heat as the physical cause of the sensation of hotness, coldness, and temperature as the degree of hotness or coldness. We know that a liquid flows only from higher to a lower level until a common level is attained, irrespective we the quantity of liquid at two levels. We replace the quantity of heat liquid with the quantity of heat and its level of temperature. We have heat flow from a body at a higher temperature to one at a lower temperature irrespective of the quantities of heat in the two bodies. This heat flow continues until the two bodies attain a common temperature. Therefore, heat can be defined as energy in transit.

The temperature of a system can be defined as the property that determines whether or not the body is in thermal equilibrium with the neighboring systems. If a number of systems are in thermal equilibrium, this common property of the system can be represented by a single numerical value called the temperature. It means that if two systems are not in thermal equilibrium, they are at different temperatures.

Measurement of temperature of a body accurately is one of the important branches of heat in physics. It also becomes necessary to measure high temperatures and low temperatures. To make this measurement possible, it is necessary to construct a suitable scale of temperature. The scale chosen must be precise and consistent and the temperatures measured on this scale must be accurate. Assessing the temperature of a body by the mere sense of touch or comparing the degree of hotness of a body with respect to another body does not help in measuring the temperature quantitatively and accurately.

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