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# Introduction to Heat Energy

Introduction
Heat is one of the essential forms of energy for the sustaining of life on earth. All matter contains heat energy in different forms. It is the energy that causes objects to warm up, and it plays a vital role in many of the natural processes that occur around us. Heat energy can transfer from one place to another because of the temperature difference. We use heat energy in our daily activities such as cooking, ironing, recreation, transportation, and much more. In this article, we will learn about what is heat, how heat works, and how heat transfers in different ways.

What is Heat?
Heat can be defined as a flow of energy from a warm to a cooler object. It is transferred from one object to another because of a temperature difference. The S.I. unit of heat is the same as that of energy, it is a joule. Other common units of heat are calorie and kilo calorie, and one calorie is equivalent to 4.18 joules. The amount of heat energy required to raise the temperature of one gram of water by one degree Celsius is called a calorie.

How Does Heat Affect Matter?
Heat affects matter in various ways. When the matter is heated, the particles of matter begin to move faster, so the distance between them increases. This process causes the matter to expand.  Conversely, when the matter is cooled, the movement of particles becomes slow, and the distance between them decreases, causing the matter to contract.

Heat can also affect the state of matter. When heat is added to the solid form of matter, its particles gain energy and begin to move faster. Consequently, the solid melts and becomes a liquid. Similarly, when more heat is provided, the liquid’s particles gain even more energy, and move faster, turning the liquid’s particles into vapors and become a gas.

Conversely, when heat is removed from the gas, its particles lose their energy and begin to move slower. This process causes the gas to condense and become a liquid. When more heat is removed, the liquid’s particles lose even more energy and move slower, causing the liquid to freeze and become a solid.

Types of Heat Energy Transfer
As mentioned above, heat energy transfers as long as there is a temperature difference. Heating the ground, boiling water, and feeling the warmth from the sun are all manifestations of heat transfer. Heat can be transferred in three different ways which are conduction, convection, and radiation.

Conduction
Conduction is the most common type of heat transfer that requires direct contact. The transfer of heat occurs due to the microscopic collision of particles and motions of electrons within the body. Conduction takes place in three basic forms of matter; solids, liquids, and gases. For instance, when you touch a hot object, you feel your hand gets warm. This is because heat is now transferred from the object to your hand through conduction.

Rubbing your hands together is another example of heat transfer through conduction. When you rub your hands together, friction occurs due to the electromagnetic attraction between charged particles on two touching surfaces. This leads to the thermal excitation of molecules in our hands, which causes the transfer of heat energy between our hands.

Fig.1 when you rub hands together, energy is transferred in the form of heat

Convection
Convection is the transfer of heat from one region to another region through the movement of fluids such as air or water. This type of heat transfer occurs in liquids and gases. For instance, when you add ice cubes to your beverage, the temperature of the liquid drops as heat transfers from liquid to ice cubes. The heat continues to move to the coldest area in the beverage until it reaches equilibrium.

Fig.2 Heat transfer through convection occurs due to the movements of fluids

Radiation is the transmission of energy through particles or electromagnetic waves. This heat transfer occurs without any direct contact between the objects. The hotter the object, the more it will radiate

Fig.3 The sun emits radiation, which heats up the earth’s surface

heat energy. For instance, the sun emits radiation, and a small portion of this energy reaches the earth in the form of light. sunlight that can reach the surface of the earth, heats the earth’s surface.

Summary
• Heat is a flow of energy that is always transferred from a hotter region to a cooler region.
• Heat can affect the state of matter whether heat is added or removed from any state, causing it to change into another form of matter.
• Conduction is a transfer of energy that requires physical contact e.g. when you touch a hot object, you feel a sensation of burning.
• Convection is a type of heat transfer through the movement of fluids such as air or water.
• Radiation is a type of transfer of heat energy through electromagnetic waves.

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