Last Updated: April 26, 2024


Temperature is a fundamental concept in physics that measures the degree of hotness or coldness of a substance or object. It plays a crucial role in various phenomena, including conduction, a mode of heat transfer characterized by the transfer of energy through direct contact between materials, and radiation, the emission or absorption of energy in the form of electromagnetic waves. Understanding temperature is essential for comprehending the behavior of matter and energy in diverse systems and processes.

What is Temperature?

Temperature is a measure of the average kinetic energy of the particles in a substance or object. It indicates how hot or cold an object is relative to a reference point, typically measured in degrees Celsius (°C), Fahrenheit (°F), or Kelvin (K). Temperature influences the physical and chemical properties of materials and plays a significant role in various natural and industrial processes.

What is the Best Example of Temperature?

One of the best examples of temperature is the measurement of body temperature in humans. Body temperature is crucial for maintaining physiological functions and is typically measured using a thermometer. Normal body temperature varies slightly from person to person but is generally around 37 degrees Celsius (98.6 degrees Fahrenheit). Deviations from this range can indicate health conditions such as fever (elevated temperature) or hypothermia (low temperature). Monitoring body temperature is essential in medical settings for diagnosing illnesses and assessing overall health.

Temperature Formulas

Celsius to Fahrenheit

F = (C×9/5)+32

where F is the temperature in Fahrenheit and C is the temperature in Celsius.

Example: Convert 20°C to Fahrenheit.

  • F = (20×95)+32
  • F = (36)+32 = 68°F

Fahrenheit to Celsius

C = (F32)×5/9

where C is the temperature in Celsius and F is the temperature in Fahrenheit.

Example: Convert 68°F to Celsius.

  • C = (68−32)×5/9​
  • C = (36)×95​=20°C

Celsius to Kelvin

K = C+273.15

where K is the temperature in Kelvin and C is the temperature in Celsius.

Example: Convert 20°C to Kelvin.

K = 20+273.15 = 293.15K

Scale of the Temperature


Celsius (°C):

  • The Celsius scale is based on the properties of water.
  • The scale assigns 0°C as the freezing point of water and 100°C as the boiling point of water at standard atmospheric pressure.
  • The Celsius scale is widely used in scientific, meteorological, and everyday applications.
  • To convert temperatures between Celsius and Fahrenheit, you can use the formula: F = (C×9/5)+32F

Fahrenheit (°F):

  • The Fahrenheit scale was developed by Daniel Gabriel Fahrenheit in the early 18th century.
  • On the Fahrenheit scale, 32°F represents the freezing point of water and 212°F represents the boiling point of water at standard atmospheric pressure.
  • The Fahrenheit scale is commonly used in the United States and some other countries, especially for weather forecasts.
  • To convert temperatures between Fahrenheit and Celsius, you can use the formula: C = (F−32)×5/9

Kelvin (K):

  • The Kelvin scale is based on absolute zero, the theoretical lowest temperature where all molecular motion ceases.
  • Absolute zero is defined as 0 Kelvin (0 K), equivalent to -273.15°C.
  • The Kelvin scale is widely used in scientific and engineering applications, especially in thermodynamics and physics.
  • Kelvin is the base unit of temperature in the International System of Units (SI).
  • To convert temperatures between Celsius and Kelvin, you can use the formula: K = C+273.15

Relationship Between Temperature and Kinetic Energy

Temperature and kinetic energy are closely related concepts in physics, particularly in the study of thermodynamics. The relationship between temperature and kinetic energy can be understood through the kinetic theory of gases, which describes how the motion of particles (atoms or molecules) in a substance contributes to its temperature.

Kinetic Theory of Gases:

  • According to the kinetic theory of gases, the temperature of a gas is a measure of the average kinetic energy of its particles.
  • Kinetic energy is the energy associated with the motion of an object, and in gases, this motion primarily consists of translational motion (movement of particles from one point to another).
  • At higher temperatures, gas particles move faster on average and thus possess higher kinetic energy. Conversely, at lower temperatures, gas particles move more slowly and have lower kinetic energy.

Mathematical Relationship:

  • The average kinetic energy (KE) of gas particles is directly proportional to the temperature (T) of the gas.
  • Mathematically, the relationship can be expressed as: KET
  • This relationship implies that as the temperature increases, the average kinetic energy of gas particles also increases, and vice versa.


  • Higher temperatures result in greater molecular motion and collisions between particles, leading to increased kinetic energy.
  • The relationship between temperature and kinetic energy is fundamental to understanding the behavior of gases, such as pressure-volume-temperature (PVT) relationships and the ideal gas law.

Experimental Confirmation:

Experimental observations support the relationship between temperature and kinetic energy. For example, heating a gas in a closed container causes an increase in pressure due to the greater kinetic energy of the gas particles.

Heat vs Temperature

Heat is a form of energy transferTemperature is a measure of hotness or
that flows from a hotter objectcoldness of an object or substance
to a colder objectheat is exchanged between a hot and cold object
Joules (J) or calories (cal)Degrees Celsius (°C), Fahrenheit (°F)
Heat is measured in terms of theTemperature is measured using
amount of energy transferredthermometers
Heating water on a stoveA thermometer reading
Melting ice into waterIce melting into water at 0°C
Boiling water to produce steamWater at 100°C boiling into steam

Temperature Measurement

Temperature measurement refers to the process of quantifying the degree of hotness or coldness of an object or substance. Several methods are used to measure temperature, each relying on different physical principles and technologies. Here’s an explanation of temperature measurement methods:

  • Thermocouples: Thermocouples utilize the Seebeck effect, where a voltage is generated at the junction of two dissimilar metals when there’s a temperature gradient.
  • Resistance Temperature Detectors (RTDs): RTDs are temperature sensors made of materials whose electrical resistance changes predictably with temperature.
  • Thermistors: Similar to RTDs, thermistors are temperature-sensitive resistors. However, thermistors exhibit a more significant change in resistance with temperature compared to RTDs, making them suitable for applications requiring high sensitivity.
  • Bimetallic Strips: Bimetallic strips consist of two different metals bonded together, each with different coefficients of thermal expansion. As temperature changes, the strip bends due to the unequal expansion of the metals.
  • Liquid-in-Glass Thermometers: These traditional thermometers consist of a glass bulb containing a liquid (such as mercury or alcohol) with a calibrated scale.
  • Infrared Thermometers: Infrared thermometers measure temperature by detecting the infrared radiation emitted by an object.
  • Pyrometers: Pyrometers are specialized instruments used to measure high temperatures, typically in industrial or scientific applications.
  • Thermographic Cameras: Also known as infrared cameras, thermographic cameras capture infrared radiation emitted by objects and convert it into thermal images.

How a Thermometer Measures Temperature

  • Thermometers measure temperature based on the principle of thermal expansion, which states that most substances expand when heated and contract when cooled.
  • In a typical liquid-in-glass thermometer, a temperature-sensitive liquid (such as mercury or alcohol) is sealed in a glass tube with a calibrated scale.
  • When the thermometer is exposed to a temperature change, the liquid expands or contracts, causing it to rise or fall within the calibrated scale.
  • The position of the liquid level on the scale corresponds to the temperature of the surroundings, allowing the temperature to be read.

Thermal Equilibrium

  • Thermal equilibrium is a state in which two or more objects or systems have the same temperature and there is no net transfer of heat between them.
  • When two objects at different temperatures are brought into contact, heat transfer occurs until thermal equilibrium is reached.
  • In thermal equilibrium, the rate of heat transfer from the hotter object to the colder object is equal to the rate of heat transfer in the opposite direction.
  • At thermal equilibrium, the temperatures of the objects are equal, and there is no further change in temperature over time.

Absolute Temperature

  • Absolute temperature is a temperature scale that begins at absolute zero, the theoretical lowest temperature at which all molecular motion ceases.
  • The Kelvin (K) scale is the most common absolute temperature scale used in scientific measurements.
  • Absolute temperature is directly proportional to the average kinetic energy of the particles in a substance. As temperature increases, so does the average kinetic energy of the particles.
  • Unlike the Celsius and Fahrenheit scales, which have arbitrary zero points, the Kelvin scale’s zero point (0 K) corresponds to absolute zero.
  • The relationship between temperature in Kelvin (K) and Celsius (°C) is given by the equation: KC+273.15.

Effects of Temperature?

Temperature has a profound impact on various aspects of the natural world and human activities. Some of the effects of temperature include:

  • Physical Changes: Temperature influences the physical state of matter, causing substances to change from solid to liquid to gas at specific temperature points (melting, freezing, and boiling points).
  • Chemical Reactions: Temperature affects the rate and outcome of chemical reactions. Higher temperatures generally increase reaction rates by providing more energy for molecules to collide and react. However, extreme temperatures can also denature proteins and alter reaction pathways.
  • Biological Processes: Temperature profoundly influences biological systems. Organisms have adapted to specific temperature ranges, and deviations from these ranges can disrupt biological processes.
  • Weather Patterns: Temperature variations drive atmospheric circulation and weather patterns on Earth. Differential heating of the atmosphere by the Sun creates areas of high and low pressure, which in turn influence wind patterns, precipitation, and climate systems.
  • Ecosystem Dynamics: Temperature influences the distribution and abundance of species in ecosystems. Changes in temperature can alter habitat suitability, migration patterns, reproductive cycles, and food availability, impacting ecosystem structure and function.
  • Material Properties: Temperature affects the mechanical, electrical, and thermal properties of materials. For instance, metals expand when heated and contract when cooled, affecting their dimensions and structural integrity. Temperature also influences the conductivity and resistance of materials.
  • Technological Applications: Temperature control is critical in various technological applications, including manufacturing, energy production, and electronics.


Why is the Kelvin scale considered an absolute temperature scale?

The Kelvin scale is considered an absolute temperature scale because its zero point, absolute zero, is the theoretical lowest temperature at which all molecular motion ceases.

What are some common applications of temperature measurement?

Temperature measurement is used in various fields, including weather forecasting, cooking, industrial processes, healthcare, and scientific research. It is essential for controlling processes, monitoring environmental conditions, and ensuring safety in many applications.

How do scientists measure temperature in outer space?

In space, scientists use instruments such as infrared telescopes and radiometers to detect thermal radiation emitted by celestial objects.

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