Energy definition may be defined as the capacity of doing any physical  work. The work must exist in potential, kinetic, chemical, thermal, or any other forms.

According to Physics, energy may be defined as a quantitative property that is used to transfer to a physical system or a body to perform any physical work on the body.

The word energy is taken from a Greek word “Energeia” which means activity or Operation.

Properties Of Energy:

1. Energy is invisible in nature but it can manifest itself through  light, wind.
2. Energy can neither be destroyed nor be created, it can only be transmitted from one form to another.
3. Sun and stars are the ultimate source of energy.
4. Universe has a constant and finite amount of energy.
5. Primary energy is a form of energy that is available in nature naturally. For Example, Energy released from the muscles of humans and animals.
6. Secondary energy is an energy carrier which is converted by humans from primary energy sources. For Example, electricity is a secondary energy generated from coal, wind and water.
7. Energy can vary with the properties such as position, mass, speed, shape, etc.
8. The law of conservation of energy was discovered by Antoine de Lavoisier in the 18th century which states that “Nothing is lost, nothing is created, everything is transformed.”
9. In International Systems of Unit (SI), Energy can be measured in Joules (J) which is equal to the work done by one newton force through a one meter distance.

Classification Of Energy:

Based on the energy source, Energy can be classified into two types as renewable and non-renewable source of energy.

• Renewable Source of Energy:

Renewable source of energy is the energy that is derived from natural processes. They are present in abundant amount on the earth and can be renewed again and again

For example, solar, wind, ocean, hydropower, biomass, hydrogen, biofuels and many more.

• Non-Renewable Source of Energy:

Non-Renewable sources of energy are present in limited amounts on the Earth. These resources can not be renewed again and again. They are produced by the decomposing plants and animals and found in the earth’s crust.

For example, coal, oil, natural gas, etc.

Types Of Energy: 

There are many specific types of energy, the two major forms include kinetic energy and potential energy.

• Kinetic Energy:

Kinetic energy is the energy which is required to move any object or mass

For example, mechanical energy, electrical energy, etc

• Potential Energy:

Potential energy is a form of energy that can be stored for future use

For example, nuclear energy, chemical energy, etc.

Forms Of Energy:

Energy can exist in different forms. Each form of energy can be transferred or converted into various other forms of energy. Some of the forms of energy are as follows:

• Chemical Energy:

Chemical energy is the energy which  is present during the formation of  bonds in any chemical reactions. Chemical energy is generally released in the form of heat during chemical reactions.

For example, chemical energy release from the burning of wood or fuels.

• Electrical Energy:

Electrical energy is the energy used by the electrons in any electric conductor. Electrical Energy is also known as Light Energy or Heat Energy or Motion Energy.

For example, lightning, power plants convert chemical energy stored in batteries into electricity.

• Mechanical Energy:

Mechanical energy is the energy through which any body or object common into motion.

For example, various machines such as drilling use mechanical energy to do work.

• Thermal Energy:

 Thermal energy is the energy which is used to increase the temperature of any subject or system.

For example, the use of solar radiation to cook food.

• Nuclear Energy:

Nuclear energy is the energy which is present inside an atom or a molecule. Nuclear energy can be produced by the fusion or fission process.

Fusion is the process in which atoms are combined to each other while fission is splitting of atoms. The fission process is widely used as compared to fusion.

There are about 35 countries in the world including India which generate electricity from nuclear sources of energy.

• Gravitational Energy:

Gravitational Energy is the Energy that is held by a body or object in a gravitational field.

For example, water falling down from a waterfall.

Hydrogen Energy:

Hydrogen is one of the ultimate sources of energy which can be used for a broad range of applications. Hydrogen energy can be a possible substitute for fossil fuels. It  is also considered as an alternative fuel which can be used for the production of electricity, heat and water for various purposes. It can also be used at the level of commercials such as in telecom towers for providing backup power. Hydrogen energy can also be used as a fuel in rockets and is very fuel efficient. The major disadvantages of hydrogen as a fuel is that it is expensive and highly flammable. Plus, it is very difficult to store.

Energy Conservation:

Energy Conservation is to conserve energy by using less energy in order to lower the costs and reduce the impact on the environment. This can be done by using less electricity, gas and other forms. Some ways to save energy include using smart power strips, use of energy efficient appliances, reducing water wastages and water heating expenses, usage of energy efficient bulbs, Installation of programmable thermostat, etc.