What is Temperature? Definition, Scales, Units, & Facts

What is Temperature? While learning about weather, seasons, or even our bodies, one word we often hear is temperature. But what is temperature? Temperature is a measure of how hot or cold something is. Whether it's checking the weather or knowing the normal temperature of the human body, temperature helps us understand our environment better and stay comfortable and safe.

To understand it better, let's learn about its definition, scales, and the unit of temperature in the simplest way.

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How to Define Temperature?

When we define temperature, we simply talk about how hot or cold something is. It helps us understand the warmth of the air, a glass of water, or even our own body. Temperature shows how heat moves from a hotter object to a cooler one. It is measured using different units of temperature like Celsius or Fahrenheit. Whether it’s checking the normal temperature of human body or the weather outside, temperature helps us in many daily activities.

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What is the Normal Temperature of Human Body?

The normal temperature of human body is usually around 98.6°F or 37°C. But this number can change a little from person to person. A healthy body temperature can be anywhere between 97°F (36.1°C) and 99°F (37.2°C). Body temperature also changes during the day. It is usually lower in the morning and higher in the evening. 

Things like exercise, sleep, age, or even changes in hormones can affect body temperature. For example, your body may feel warmer after playing outside or cooler while sleeping. If the body temperature goes above 100.4°F (38°C), it is usually called a fever. This can happen when someone is sick or fighting an infection.

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SI Unit of Temperature

The SI unit of temperature is Kelvin (K). It is the standard unit used in science to measure how hot or cold something is. Scientists all over the world use Kelvin to keep measurements the same and easy to compare.

Even though we mostly use Celsius (°C) in daily life, like for weather or body temperature, Kelvin is used in labs and physics. If you're wondering what is the SI unit of temperature, it's Kelvin, and it always starts from absolute zero, which is the coldest temperature possible.

Units of Temperature

Temperature can be measured using different units. The three main units used for temperature are Celsius (°C), Fahrenheit (°F), and Kelvin (K). Among these, Kelvin is the SI unit of temperature, while Celsius and Fahrenheit are more commonly used in daily life. Let's discuss them one by one.

• Celsius: The Celsius scale was created by Anders Celsius, a Swedish scientist, in 1742. This scale is based on the freezing point of water at 0°C and the boiling point at 100°C. The Celsius unit uses the symbol °C. For example, the normal temperature of the human body is about 37°C.

• Fahrenheit: The Fahrenheit scale was developed by Daniel Gabriel Fahrenheit. On this scale, water freezes at 32°F and boils at 212°F. The symbol used for Fahrenheit is °F. The usual body temperature in Fahrenheit is about 98.6°F.

• Kelvin: Kelvin is the standard unit of temperature in the International System of Units (SI). It is named after the physicist William Thomson, also known as Lord Kelvin. Unlike Celsius and Fahrenheit, Kelvin does not use the degree (°) symbol. The Kelvin scale starts at absolute zero, which is the lowest possible temperature.

Each unit has its use depending on the situation, but Kelvin is mostly used in science, while Celsius and Fahrenheit are used in everyday life.

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Relation Between Celsius and Fahrenheit

• To convert Celsius to Fahrenheit: F = (C × 9/5) + 32.

• To convert Fahrenheit to Celsius: C = (F − 32) × 5/9.

Relation Between Celsius and Kelvin

• To convert Celsius to Kelvin: K = C + 273.15.

• To convert Kelvin to Celsius: C = K − 273.15.

Temperature Conversion Formulas

Temperature conversion formulas help us change the temperature value from one unit to another. This is useful because temperature can be measured in different units like Celsius, Fahrenheit, and Kelvin. Using these formulas, one can easily convert temperature readings between these scales. Find out the important temperature conversion formulas here:

• Celsius to Kelvin: K = C + 273.15

• Kelvin to Celsius: C = K - 273.15

• Fahrenheit to Celsius: C = (F - 32) × (5/9)

• Celsius to Fahrenheit: F = C × (9/5) + 32

• Fahrenheit to Kelvin: K = (F - 32) × (5/9) + 273.15

• Kelvin to Fahrenheit: F = (K - 273.15) × (9/5) + 32

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These formulas make it simple for students and learners to convert temperatures correctly, whether they are studying, conducting experiments, or trying to understand how hot or cold something is in a different unit. Besides Celsius, Fahrenheit, and Kelvin, there are some less common temperature units like Rankine, Newton, Rømer, Réaumur, and Delisle. These units are used in certain scientific fields or historical contexts.

• Rankine:

• From Celsius to Rankine: °R = (°C + 273.15) × 9/5

• From Rankine to Celsius: °C = (°R − 491.67) × 5/9

• Newton:

• From Celsius to Newton: °N = °C × 33/100

• From Newton to Celsius: °C = °N × 100/33

• Rømer:

• From Celsius to Rømer: °Rø = (°C × 21/40) + 7.5

• From Rømer to Celsius: °C = (°Rø − 7.5) × 40/21

• Réaumur:

• From Celsius to Réaumur: °Ré = °C × ⅘

• From Réaumur to Celsius: °C = °Ré × 5/4

• Delisle:

• From Celsius to Delisle: °De = (100 − °C) × 3/2

• From Delisle to Celsius: °C = 100 − (°De × 2/3)

Difference Between Heat and Temperature

Heat and temperature are closely related but they are not the same. Many students often confuse the two, so it's important to understand how they differ.

Temperature is a measure of how hot or cold something is. It tells us the average kinetic energy of the particles present in a substance.

• In simple words, temperature shows how fast or slow the particles are moving. If the particles move very fast, the temperature is high; if they move slowly, the temperature is low.

• Temperature is measured using thermometers, and it is expressed in units like Celsius (°C), Fahrenheit (°F), or Kelvin (K).

On the other hand, heat is the energy that flows from one object to another due to a difference in temperature.

• When two objects are at different temperatures, heat always flows from the hotter object to the colder one.

• This flow of energy continues until both objects reach the same temperature. Heat is a form of energy and is measured in units like joules (J) or calories.

Practice Questions on Temperature Conversion Formulas

Now that you have learned what temperature is and how it is measured in different units like Celsius, Fahrenheit, and Kelvin, it's time to check your understanding. Try solving these practice questions to make your concept stronger and boost your confidence.

Q.1. Convert 25°C into Kelvin.

Solution: Given, C = 25°C
Use the formula:
K = C + 273.15
K = 25 + 273.15 = 298.15 K

Q.2. What is 212°F in Celsius?

Solution: Given, F = 212°F
Use the formula:
C = (F − 32) × 5/9
C = (212 − 32) × 5/9
C = (180) × 5/9 = 100°C

Q.3. Convert 0°C into Fahrenheit.

Solution: Given, C = 0°C
Use the formula:
F = (C × 9/5) + 32
F = (0 × 9/5) + 32 = 32°F

Q.4. What is the temperature in Kelvin if it is 50°F?

Solution: Given, F = 50°F
Use the formula:
K = (F − 32) × 5/9 + 273.15
K = (50 − 32) × 5/9 + 273.15
K = (18 × 5/9) + 273.15 = 10 + 273.15 = 283.15 K

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