Temperature

What Is Temperature?

Temperature is a measure of how hot or how cold something is. It tells us how much heat energy is in an object or in the air. When temperature is high, things feel hot. When temperature is low, things feel cold.

We use temperature every day. We check it to decide what clothes to wear, to cook food safely, to store medicine in a fridge, and to control heating and air conditioning at home or school.

Definition

In simple science language, temperature shows how fast the tiny particles inside a substance are moving. When particles move faster, the temperature is higher. When they move slower, the temperature is lower.

More formal definition. Temperature is a physical quantity that shows how hot or cold a body is compared with a chosen scale, such as Celsius, Fahrenheit, or Kelvin.

The main points to remember are.

• High temperature means hot
• Low temperature means cold
• Equal temperature means no net flow of heat between two objects in contact

History / Origin

People have always felt hot and cold, but they did not always have numbers to describe it. Long ago, people used simple words like warm, cool, or freezing. Later, scientists wanted a way to measure temperature in a clear and repeatable way.

Important steps in the history of temperature measurement.

• Early thermoscopes. In the 1600s, simple glass devices showed when air got hotter or colder, but they did not have a fixed scale or numbers.
• Fahrenheit scale. In the early 1700s, Daniel Gabriel Fahrenheit made better thermometers using mercury. He created the Fahrenheit scale, where water freezes at 32 degrees Fahrenheit and boils at 212 degrees Fahrenheit.
• Celsius scale. Around 1740s, Anders Celsius designed a scale based on water. In this scale, water freezes at 0 degrees Celsius and boils at 100 degrees Celsius at normal air pressure.
• Kelvin scale. In the 1800s, Lord Kelvin introduced the Kelvin scale. It starts at absolute zero, which is the lowest possible temperature where particle motion is minimal. This is useful in physics and space science.

Today, these temperature scales are used worldwide in different fields such as weather, medicine, cooking, engineering, and space research.

Symbol & Abbreviation

Several symbols are used when we talk about temperature.

• T. The general symbol for temperature in formulas and science writing.
• t. Sometimes used for temperature in engineering, but T is more common.

Common temperature units and how we write them.

• Degree Celsius. Written as degrees Celsius or deg C. The symbol is b0C.
• Degree Fahrenheit. Written as degrees Fahrenheit or deg F. The symbol is b0F.
• Kelvin. Written as kelvin. The symbol is K. There is no degree sign for kelvin.
• Rankine. Less common. Used mainly in some engineering fields, especially in the United States. Symbol is R or sometimes b0R.

Example. A body temperature of thirty seven degrees Celsius is written as 37b0C.

Current Use Around the World

Different temperature units are popular in different places and for different jobs.

• Celsius (b0C)
  • Used in most countries for daily life.
  • Used on weather reports, in schools, and on most modern thermometers.
  • Used in science, except in some special areas that use kelvin.
• Fahrenheit (b0F)
  • Used mainly in the United States and a few other places for everyday weather and home use.
  • Common on older ovens and air conditioning units in the US.
• Kelvin (K)
  • Used in physics, chemistry, and space science.
  • Used to describe very hot or very cold things, such as stars, outer space, and experiments with gases.
  • Always used without the degree sign.
• Rankine (R)
  • Used in some engineering fields, such as older thermodynamic calculations in the US.
  • Not common in everyday life.

In international science and engineering, Celsius and Kelvin are the most important scales. For daily weather reports, most of the world uses Celsius, while the United States prefers Fahrenheit.

Example Conversions

Here are some useful rules and examples for converting temperature between different units. Remember to keep the units correct in every step.

Between Celsius and Fahrenheit

• From Celsius to Fahrenheit. F = (C d7 9 5) + 32
• From Fahrenheit to Celsius. C = (F d7 5 9) d7 32

Examples.

• 0b0C = (0 d7 9 5) + 32 = 32b0F
• 100b0C = (100 d7 9 5) + 32 = 212b0F
• 68b0F = (68 d7 5 9) d7 32 = 20b0C
• 98.6b0F (normal body temperature) b0C = (98.6 d7 5 9) d7 32 d7 37b0C (about)

Between Celsius and Kelvin

• From Celsius to Kelvin. K = C + 273.15
• From Kelvin to Celsius. C = K d7 273.15

Examples.

• 0b0C = 273.15 K
• 25b0C = 25 + 273.15 = 298.15 K
• 300 K = 300 d7 273.15 = 26.85b0C (about 27b0C)

Between Fahrenheit and Kelvin

You can convert using one long step, or go through Celsius first.

• Direct formula. K = (F + 459.67) d7 5 9
• Via Celsius. First convert F to C, then add 273.15 to get K.

Examples.

• 32b0F. C = (32 d7 5 9) d7 32 = 0b0C, so K = 0 + 273.15 = 273.15 K
• 212b0F. C = (212 d7 5 9) d7 32 = 100b0C, so K = 100 + 273.15 = 373.15 K

Related Units

Temperature is closely linked to several related units and concepts.

• Degree Celsius (b0C). A metric temperature unit based on water freezing at 0b0C and boiling at 100b0C at normal pressure.
• Degree Fahrenheit (b0F). A temperature unit mainly used in the United States. Water freezes at 32b0F and boils at 212b0F.
• Kelvin (K). The SI base unit for temperature. Often used in science and engineering.
• Rankine (R). An absolute temperature scale related to Fahrenheit, used in some engineering areas.
• Heat energy (joule, J). Not the same as temperature. Heat is energy that flows because of a temperature difference.
• Thermal conductivity. A property that tells how easily heat passes through a material, affected by temperature.
• Specific heat capacity. Tells how much energy is needed to change the temperature of a substance.

FAQs

Q. What is the simple meaning of temperature
A. Temperature is a number that shows how hot or how cold something is. Higher numbers mean hotter, lower numbers mean colder.

Q. What is the SI unit of temperature
A. The SI base unit of temperature is the kelvin, written with the symbol K. In everyday life, we more often use degrees Celsius, written as b0C.

Q. What is the difference between temperature and heat
A. Temperature tells how hot or cold something is. Heat is energy that moves from a hotter place to a colder place because of a temperature difference. Two objects can have the same temperature but different amounts of heat energy if their sizes or materials are different.

Q. Why do some countries use Celsius and others use Fahrenheit
A. Most countries use Celsius because it fits well with the metric system and is based on water freezing and boiling points. The United States continues to use Fahrenheit because of historical reasons and because many people are used to it in daily life.

Q. What is normal human body temperature
A. Normal body temperature is about 37b0C, which is about 98.6b0F. Some people are a little higher or lower, and that can still be healthy.

Q. What is absolute zero
A. Absolute zero is the lowest possible temperature, 0 K or about d7 273.15b0C. At this temperature, particles have as little motion as they can. It is not possible to reach absolute zero exactly, but scientists can get very close in special labs.

Q. Why is Kelvin used without the degree sign
A. Kelvin is defined as an absolute scale in the SI system, so it is written simply as K, not b0K. This makes it easier to use in scientific formulas and calculations.

Q. Can temperature be negative
A. Yes. On the Celsius and Fahrenheit scales, temperatures can go below zero, which means very cold. On the kelvin scale, temperatures cannot go below 0 K, because that is absolute zero.