What is Heat? All matter is made up of molecules and atoms. These atoms are always in different types of motion (translation, rotational, vibrational). The motion of atoms and molecules creates heat or thermal energy. All matter has this thermal energy. The more motion the atoms or molecules have the more heat or thermal energy they will have. This is an animation made from a short molecular dynamics simulation of water. The green lines represent hydrogen bonds between oxygen and hydrogen. Notice the tight structure of water Hydrogen bonds are much weaker than covalent bonds. However, when a large number of hydrogen bonds act in unison they will make a strong contributory effect. This is the case in water shown here. Liquid water has a partially ordered structure in which hydrogen bonds are constantly being formed and breaking up. Because of the short time scale (on the order of a few picoseconds) few bonds What is temperature? From the video above that shows movement of atoms and molecules it can be seen that some move faster than others. Temperature is an average value of energy for all the atoms and molecules in a given system. Temperature is independent of how much matter there is in the system. It is simply an average of the energy in the system. How is heat transferred? Heat can travel from one place to another in three ways: Conduction, Convection and Radiation. Both conduction and convection require matter to transfer heat. If there is a temperature difference between two systems heat will always find a way to transfer from the higher to lower system. CONDUCTION-- Conduction is the transfer of heat between substances that are in direct contact with each other. The better the conductor, the more rapidly heat will be transferred. Metal is a good conduction of heat. Conduction occurs when a substance is heated, particles will gain more energy, and vibrate more. These molecules then bump into nearby particles and transfer some of their energy to them. This then continues and passes the energy from the hot end down to the colder end of the substance. CONVECTION-- Thermal energy is transferred from hot places to cold places by convection. Convection occurs when warmer areas of a liquid or gas rise to cooler areas in the liquid or gas. Cooler liquid or gas then takes the place of the warmer areas which have risen higher. This results in a continous circulation pattern. Water boiling in a pan is a good example of these convection currents. Another good example of convection is in the atmosphere. The earth's surface is warmed by the sun, the warm air rises and cool air moves in. RADIATION-- Radiation is a method of heat transfer that does not rely upon any contact between the heat source and the heated object as is the case with conduction and convection. Heat can be transmitted through empty space by thermal radiation often called infrared radiation. This is a type electromagnetic radiation . No mass is exchanged and no medium is required in the process of radiation. Examples of radiation is the heat from the sun, or heat released from the filament of a light bulb. SOURCES AND READERS CHOICES -- Heat and Temperature from Cool Cosmo -- NASA Here is a good applet to show motion in molecules -- you can control the temperature and see in this applet how to movements of the molecules change. Important Temperatures in Cooking and Culinary Skills
In order to continue enjoying our site, we ask that you confirm your identity as a human. Thank you very much for your cooperation. Any matter which is made up of atoms and molecules has the ability to transfer heat. The atoms are in different types of motion at any time. The motion of molecules and atoms is responsible for heat or thermal energy and every matter has this thermal energy. The more the motion of molecules, more will be the heat energy. However, talking about heat transfer, it is nothing but the process of transfer of heat from a high-temperature body to a low temperature one. According to thermodynamic systems, heat transfer is defined as “The movement of heat across the border of the system due to a difference in temperature between the system and its surroundings.” Interestingly, the difference in temperature is said to be a ‘potential’ that causes the transfer of heat from one point to another.
Heat can travel from one place to another in several ways. The different modes of heat transfer include:
Meanwhile, if the temperature difference exists between the two systems, heat will find a way to transfer from the higher to the lower system. 
Conduction is defined as
An area of higher kinetic energy transfers thermal energy towards the lower kinetic energy area. High-speed particles clash with particles moving at a slow speed, as a result, slow speed particles increase their kinetic energy. This is a typical form of heat transfer and takes place through physical contact. Conduction is also known as thermal conduction or heat conduction.
The rate of conduction can be calculated by the following equation:
Where,
The coefficient of thermal conductivity shows that a metal body conducts heat better when it comes to conduction.
Following are the examples of conduction:
Convection is defined as
As the temperature of the liquid increases, the liquid’s volume also has to increase by the same factor and this effect is known as displacement. The equation to calculate the rate of convection is as follows: Where,
Examples of convection include:
Learn more about Convection
Radiant heat is present in some or other form in our daily lives. Thermal radiations are referred to as radiant heat. Thermal radiation is generated by the emission of electromagnetic waves. These waves carry away the energy from the emitting body. Radiation takes place through a vacuum or transparent medium which can be either solid or liquid. Thermal radiation is the result of the random motion of molecules in matter. The movement of charged electrons and protons is responsible for the emission of electromagnetic radiation. Let us know more about radiation heat transfer. Radiation heat transfer is measured by a device known as thermocouple. A thermocouple is used for measuring the temperature. In this device sometimes, error takes place while measuring the temperature through radiation heat transfer.
As temperature rises, the wavelength in the spectra of the radiation emitted decreases and shorter wavelengths radiations are emitted. Thermal radiation can be calculated by Stefan-Boltzmann law:
Where,
Following are the examples of radiation:
To know more about heat transfer in detail, click on the video below.
The different modes of heat transfer are:
Example: UV rays coming from the sun.
SI unit of heat is Joules. Electromagnetic radiations are emitted through the movement of charged electrons and protons.
It is known as convection.
Put your understanding of this concept to test by answering a few MCQs. Click ‘Start Quiz’ to begin! Select the correct answer and click on the “Finish” button
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What are the three basic mechanisms of heat transfer and how are they related to the atmosphere?
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