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What is Heat Energy? - Facts & Calculation

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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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Lesson Transcript
Instructor: Richard Cardenas

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

In this lesson, you will learn about heat and that heat is a form of energy. You will learn about the properties of heat and the equations that will help you calculate heat in a variety of situations.

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.

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.

Conduction

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.

Conduction

Convection

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.

Convection

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.

Radiation

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.

Another interesting fact about heat is that different substances absorb as well as give off heat in varying amounts. For example, consider boiling water. Before the water boils, you can still put your hand in the water, but you can't touch the pot. What does this mean? Water takes longer to absorb heat than the metal pot containing the water. This is because the water and the pot each have a different specific heat capacity, which is the amount of heat needed to raise the temperature of a specific mass by a specific amount. Metals have a low specific heat capacity, and liquids like water have a higher specific heat capacity. This means that metals will heat up and cool down quicker than water. So, when the temperature of a substance changes, we can calculate the amount of heat transferred if we know the specific heat capacity and the mass of the substance.

The formula for heat is then:

Equation

In this equation, m is the mass of the substance and c is the specific heat capacity of the substance. The table here is a list of specific heats for a few substances:

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