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What is Heat Energy?-Definition, Unit, Sources, And Examples

August 24, 2022
written by Adeel Abbas

The transfer of energy from a high-temperature body to a lower-temperature one is called heat energy.

What is heat energy?

The motion of particles like atoms, ions, and molecules to liquids causes the production of heat energy. The difference in temperature between the two systems leads to heat transfer from one system to another.

The first law of thermodynamics states that the change in internal energy of a closed system is the same as the amount of heat Q supplied to the system. The second law of thermodynamics tells about heat and loss in its conversion.

Higher temperatures cause particles to have higher energy. Some of the energy can be transmitted to other particles at a lower temperature. When a fast traveling particle collides with a slower particle in the gas state, it transfers its energy to the other particle, and thus increases the speed of slow-moving particles.

When billions of particles collide with each other, a region of high energy transfers across the material until a condition of thermal equilibrium is developed. The temperature across the material is not different.

Heat Energy Unit

The International System of Units (SI) has the unit joule in it as a form of energy. The British thermal unit and the calories are often used in applied fields of engineering. The unit for the rate of heat transfer is the watt, which is defined as one joule per second.

Calorie1 cal4.184 J
Joules1 J0.000239006 kcal / 0.000947817Btu
BTU1 Btu1055.06 J

Sources of Heat

There are different types of energy in nature like mechanical energy, sound energy, light energy, electric energy, tidal energy, heat energy, and so on. The transfer of heat from a warm system to a cool system results in heat energy being generated.

In our day-to-day activities like cooking, heating, ironing, and so on, heat energy is an important form of energy. A source of heat energy is an object or system that gets heat from something. Some of the major sources of heat energy can be found here.


Our planet is fired with light and life every second of every day by the Sun, but we cannot always see it. the sun is a living source of heat energy.


The heat energy that is obtained from Earth is called geothermal energy. It can be found in the water and under the ground. It is possible to find heat in the form of molten rocks and magma inside the Earth’s crust.


Electric energy can be converted into heat energy. Some of the devices that convert electrical energy into heat energy are the iron, water heater, and induction cooker. The principle of the heating effect of electric current is used to derive this.

Heat Energy Examples

  • In our solar system, the Sun is the largest source of heat energy. In the form of radiation, it emits heat that reaches Earth.
  • When the gas is burned, a stovetop acts as a source of heat energy. Anything that is placed above the stove becomes a source of energy to cook.
  • The heat energy comes from the source of automobile fuels. The fuel provides energy for the vehicle’s motion when it burns.
  • A hot cup of coffee or tea has heat energy in it.