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What is Heat Energy? - Facts & Calculation

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Instructor: Richard Cardenas

Richard Cardenas has taught Physics for 15 years. He has a Ph.D. in Physics with a focus on Biological Physics.

Heat energy refers to how fast atoms and molecules move to create high temperatures in objects. Study the definition of heat energy, facts about heat energy, conduction, convection, radiation, and the calculation of the formula for heat. Updated: 03/04/2022

Definition of Heat Energy

Heat has always been a mystery. Antoine Lavoisier theorized that heat was a substance with mass. That meant that heat transfer involved the transfer of an actual substance between bodies. Unfortunately, Lavoisier's theory was not supported by experimental observation, so a better description of heat was needed.

Heat has always been confused with temperature, but the reason is that heat and temperature are related. Temperature is a quantitative measure of hotness or coldness. Solids, liquids, and gases are made up of atoms and molecules. When these atoms and molecules are moving slowly, then the temperature of that substance would be low. The faster the atoms and molecules move, the higher the temperature. Heat is the total energy of these atoms and molecules as they move. This figure shows how the speed of the atoms and molecules is related to the temperature of the substance.

heat diagram

The total energy of the atoms and molecules shown in the figure onscreen is what we call heat.

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  • 0:00 Definition of Heat Energy
  • 1:05 Facts About Heat Energy
  • 1:33 Conduction
  • 2:40 Convection
  • 3:13 Radiation
  • 6:01 Lesson Summary
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Facts About Heat Energy

Here are some interesting facts and properties of heat energy. The figure here illustrates the direction of heat transfer between two substances.

heat transfer

Heat transfer is when heat energy flows from the object of higher temperature to an object with a lower temperature. It will never do the reverse.

Heat energy can be transferred by the following methods: conduction, convection, and radiation.


Let's first look at the process of heat transfer by conduction. Consider the following situation, which you may have experienced. You have a cup of very hot coffee, and you put sugar into the coffee and use a spoon to stir the coffee. You accidentally left the spoon in the coffee when you left it on your table. Minutes later, you grab the spoon from the coffee and notice the spoon is now hot. The spoon, which was initially cold, is now nearly as hot as the coffee. This situation is an illustration of conduction. The molecules of the spoon immersed in the coffee were forced to move faster. These faster moving molecules bump into adjacent slower moving molecules and cause them to move faster, etc. After some time, all of the spoon molecules will be moving faster. Conduction is a process of heat transfer where the faster moving molecules impart their energy to slower moving molecules until the entire substance is moving with a faster speed. The figure you're looking at onscreen illustrates conduction.



The second heat transfer method is called convection. Ever hear of the statement that warm air rises? This statement describes convection. Convection, illustrated in the figure here, is the method of heat transfer that involves large masses of a substance circulating because of the temperature differences within that substance.


As the warmer mass rises, the cooler mass moves down and in the process heat is transferred to the cooler mass which causes it to move up.


The third heat transfer mechanism is called radiation. Radiation is the method that allows us to get heat from the sun. Through radiation, the sun is able to transfer energy to the Earth even through the vacuum of space. Also, every object gives off radiation. You give off radiation, your dog gives off radiation, and even an ice cube gives off radiation. If you put a piece of metal into a fire and take it out after a few minutes, the piece of metal will glow. This is an example of radiation. The sun sends us radiation in a short wave, and the earth emits the radiation in a long wave.

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