Definition of temperature

Introduction

We all have used the word “temperature” in our daily lives and have developed a common notion for the same, i.e., to refer to hotness or coldness. Hence, when we say that something is hot or cold, we generally use a reference point to express the relative degree of hotness or coldness of a body. For example, when we say ice cream is colder than tea, we use tea as a reference point to determine the temperature or the relative coldness of ice cream. Thus in simple words, the temperature can be referred to as the measure of the degree of hotness or coldness of a body.

Defining Temperature

Many people think that temperature is a form of energy, which is simply not true. In fact, it is a measurement that shows the average kinetic energy in one atom or molecule. Before the evolution of such measurement concepts, the temperature was determined on the basis of human perception, i.e. the temperature was usually determined by human touch. However, such measurement is not accurate. For example, a wooden deck might seem to be warmer than a metal cup. Even though both have an equal temperature based on the external atmosphere, metal being a good conductor of heat, draws out heat from your body faster when you touch it than wood, which is a poor conductor of heat. A simple temperature definition could be a physical measurement of hotness or coldness using a thermometer, but the temperature is closely related to the kinetic energies of the atoms and molecules of an object.

Temperature and Kinetic Energy

We have talked about how temperature is a measurement of the average kinetic energy of an atom or molecule, but what is kinetic energy? In simple terms, kinetic energy is a type of energy that exists in a body due to its motion. We can see a range of kinetic energy in molecules because all molecules move at a different speed. This molecular motion is influenced by heat. When an object absorbs heat, the molecules of such an object move faster, increasing the average kinetic energy that raises the temperature. 

Solids, liquids, and gases all have their temperatures. However, when their molecules vibrate faster, their temperature rises. 

Temperature Measurement

There are gadgets that measure temperature indirectly by measuring the expansion of a material. Thermometers are one type of such instrument. It is the most common tool for measuring temperature. 

One of the most basic thermometers would be a liquid thermometer. They are made up of a thin glass tube with a small amount of mercury within them. They are the devices that measure the temperature as a result of thermal expansion. Thermal expansion can be defined as an increase in the volume of a substance as the temperature rises. A tiny change in temperature causes a liquid’s volume to vary. However, this effect is amplified when the liquid swells within the thin tube of the thermometer.

Temperature scales

A thermometer can measure temperature in various well-defined scales. 

Celsius Scale and Fahrenheit Scale

On the Celsius scale, water freezes at 0°C and boils at 100°C on the Celsius scale. On the Fahrenheit scale, water freezes at 32°F and boils at 212°F. 

Kelvin Scale

In science, the Kelvin scale is the most extensively used temperature scale. It’s an absolute temperature scale with 0K, which is the coldest temperature possible. On this scale, water freezes at 273.15 K and boils at 373.15K. The Kelvin scale is an absolute scale, unlike other temperature scales. It is extensively utilized in scientific research. There is no negative temperature on the Kelvin scale because it has a perfect zero. 

Relationship between different Temperature Scales

Temperature Inversion

Usually, with an increase in elevation, the temperature decreases. It is termed a normal lapse rate. The condition can sometimes be reversed, and the normal lapse rate is inverted. The phenomenon is known as temperature inversion. Inversion is a common and short-term phenomenon. An excellent environment for inversion is a long winter night with clear skies and steady air.

There are four kinds of temperature inversions, namely –

• Surface Temperature Inversion: It is formed when air is cooled by contact with a colder surface until it is cooler than the overlying atmosphere. It often occurs on clear nights when the ground cools quickly due to radiation.
• Subsidence Inversion: A temperature inversion occurs when the air at higher altitudes gets warmer than the air at lower altitudes. Such type of temperature inversion is known as subsidence inversion.
• Valley Inversion: During the night, cold air at the hills and mountains becomes heavy and dense. Subsequently, cold air travels down the slope much like water, accumulating firmly at the bottom of valleys.
• Frontal Inversion: When the warm and cold fronts collide, the warm front rises, while the cold front descends because it’s heavy.

Conclusion

• Temperature can be referred to as the measure of the degree of hotness or coldness of a body.
• Many people think that temperature is a form of energy, which is simply not true. In fact, it is a measurement that shows the average kinetic energy in one atom or molecule.
• We can measure temperature using a tool called a thermometer in various temperature scales. The most common of such scales are Celsius, Fahrenheit, and Kelvin.
• Kelvin is the absolute measurement scale with no negative value.
• Sometimes, the normal lapse rate is inverted, and the temperature rises with rising elevation. This phenomenon is known as temperature inversion.