### Theory:

In our daily lives, we observe a variety of objects. Some of them are cold, while others are hot. At times, the two objects may be equally hot or cold. However, their degrees of hotness or coldness will differ.

Normally, a physical quantity that expresses the degree of hotness or coldness of a substance is known as temperature.
When a heat energy is applied to a substance, its temperature will rise. Similarly, when a heat energy is withdrawn from a substance, its temperature will drop.
Temperature is a measure of the average kinetic energy of the particles in a system. Its SI unit is Kelvin.
Kinetic energy is known as the energy possessed by a body with respect to its motion.
Thermometer
Generally, a thermometer is an instrument that measures the temperature of an object.

Thermometers are calibrated with some standard scales. The scales that are commonly used to measure the temperature are
• Celsius
• Fahrenheit
• Kelvin
Applications of temperature scales
• The Celsius scale is mainly used for weather forecasting.
• The Fahrenheit scale is commonly seen in clinical thermometers, which measures the human body temperature. This unit is widely used in the United States and its territories.
• Scientists in laboratories use the Kelvin scale for conducting experiments.
Important!
The normal temperature of the human body in the different temperature scales are,

Celsius - $$36$$ to $$37$$ °$$C$$
Fahrenheit - $$97$$ to $$99$$ °$$F$$
Kelvin - $$309$$ to $$310$$ $$K$$