Energy and Types of Energy

Energy is a universal term we use a lot in our daily life. Although used loosely quite often, energy has a specific physical meaning. In physics, we define energy as the ability of something to do work. Energy can exist in many forms. All forms of energy are either kinetic or potential. In this article, let us understand what energy is and the different types of energy in detail.

Table of Contents:

What Is Energy?

There are different forms of energy on earth. The sun is considered the elemental form of energy on earth. In physics, energy is considered a quantitative property that can be transferred from an object to perform work. Hence, we can define energy as the strength to do any kind of physical activity. Thus, in simple words, we can define energy as,

Energy is the ability to do work

According to the laws of conservation of energy, “ energy can neither be created nor destroyed but can only be converted from one form to another”. The SI unit of energy is Joule.

Forms of Energy

Units of Energy

The International System of Units of measurement of energy is joule. The unit of energy is named after James Prescott Joule. Joule is a derived unit equal to the energy expended in applying a force of one newton through a distance of one meter. However, energy is also expressed in many other units not part of the SI, such as ergs, calories, British Thermal Units, kilowatt-hours, and kilocalories, which require a conversion factor when expressed in SI units.

Read More: Unit of Energy

Different Types of Energy

Although there are many forms of energy, it is broadly categorized into:

  1. Kinetic Energy 
  2. Potential Energy

Forms of Energy

Kinetic Energy

Kinetic energy is the energy associated with the object’s motion. Objects in motion are capable of causing a change or are capable of doing work. To better understand, let us think of a wrecking ball. A wrecking ball in motion is used to do work such as the demolition of buildings, stones, etc. Even a slow-moving wrecking ball is capable of causing a lot of damage to another object, such as an empty house. However, a wrecking ball that is not in motion does not do any work.
Another example of kinetic energy is the energy associated with the constant, random bouncing of atoms or molecules. This is also known as thermal energy. The average thermal energy of a group of molecules is what we call temperature, and when thermal energy is transferred between two objects, it’s known as heat.

Kinetic energy is determined by the given formula

\(\begin{array}{l}K.E=\frac{1}{2}mv^2\end{array} \)

Read more: Kinetic Energy

Different Types of Kinetic Energy:

Radiant energy

  • Radiant energy is the type of energy that travels by waves or particles. This energy is created through electromagnetic waves and is most commonly experienced by humans in the form of heat. Following are a few examples of radiant energy:
  • When you turn on an incandescent light bulb, it gives off two forms of energy. There is visible light and heat that is generated. Both these generated energies are a form of radiant energy.
  • Sunlight is an example of radiant energy.

Thermal Energy

Thermal energy is similar to radiant energy and is experienced in the form of heat or warmth. While radiant energy refers to waves or particles, thermal energy describes the activity level among the atoms and molecules in an object. This is the only difference between radiant energy and thermal energy. Some examples of thermal energy include:

  • The geothermal energy that comes from the decay of natural minerals and the volcanic action of the earth is an example of thermal energy.
  • When you heat up the pizza in the oven, you raise the pizza’s temperature. The molecules that make up the pizza move more quickly when the pizza is piping hot.
  • The warmth you feel emanating from the engine is an example of thermal energy.

Sound Energy

Humans experience the vibrations that reach the human ear as sound. The disturbance moves in the form of waves through a medium like air and reaches our eardrum. On reaching the eardrum, these vibrations are converted into electrical signals and sent to the brain, which we interpret as the sensation of sound.

Electrical Energy

The flow of negatively charged electrons around a circuit results in electricity which we more commonly refer to as electrical energy.

Mechanical Energy

Mechanical energy is the energy associated with the mechanical movement of objects. This type of energy can also be referred to as motion energy.

Potential Energy

Potential energy is the energy stored in an object or system of objects. Potential energy can transform into a more obvious form of kinetic energy.

Potential energy is determined by the given formula

\(\begin{array}{l}Potential\,Energy=m\times g\times h\end{array} \)

Both potential energy and kinetic energy form mechanical energy.

Mechanical energy is determined by the following formula

\(\begin{array}{l}Mechanical\,Energy=\frac{1}{2}mv^2+mgh\end{array} \)

Different Types Of Potential Energy

Gravitational Potential Energy

Gravitational potential energy is the energy stored in an object due to its vertical position or height. A book on a high bookshelf has a higher gravitational potential energy than a book on the bottom bookshelf.

Gravitational Potential Energy Examples

  • River water at the top of a waterfall
  • A book on a table before it falls
  • A car that is parked at the top of a hill

Gravitational Potential Energy – Video Lecture

Elastic Potential Energy

Elastic potential energy is stored as a result of applying a force to deform an elastic object. The energy is stored until the force is removed and the object springs back to its original shape, doing work in the process. The deformation could involve compressing, stretching or twisting the object.

Elastic Potential Energy Examples

  • A spring that is coiled
  • The string of an archer’s bow is pulled back
  • Rubber band that has been stretched

Chemical Potential Energy

Chemical potential energy is the energy stored in the chemical bonds of the substance. The energy can be absorbed and released due to a change in the particle number of the given species.

Chemical Potential Energy Examples

  • Before the sun shines on the green leaves (potential photosynthesis)
  • Gasoline before it is ignited
  • Fireworks before they are launched

Electric Potential Energy

Electric potential energy is the energy that is needed to move a charge against an electric field.

Electric Potential Energy Examples

  • An incandescent light bulb that is turned off
  • A radio tower that is not working
  • A black-light turned off
  • A television before it is turned on

Energy Conversion: Transfer and Transform

We know energy can be transferred from one form to another. The movement of energy from one location to another is known as energy transfer. We notice various energy transformations happening around us.

Following are the four ways through which energy can be transferred:

  • Mechanically – By the action of force
  • Electrically – Electrically
  • By Radiation – By Light waves or Sound waves
  • By Heating – By conduction, convection, or radiation

The process which results in the energy changing from one form to another is known as energy transformation. While energy can be transformed or transferred, the total amount of energy does not change ­– this is called energy conservation.

Read More: Energy Conversion

Law of Conservation of Energy

The law of energy conservation is one of physics’s basic laws. It governs the microscopic motion of individual atoms in a chemical reaction. The law of conservation of energy states that “In a closed system, i.e., a system that is isolated from its surroundings, the total energy of the system is conserved.” According to the law, the total energy in a system is conserved even though energy transformation occurs. Energy can neither be created nor destroyed, it can only be converted from one form to another.

Read More: Law of Conservation of Energy

Video Lecture on Kinetic Energy and Potential Energy

Frequently Asked Questions – FAQs


What happens to the total energy of the object falling freely towards the ground?

The energy remains constant.

What happens to the energy of a body on which work is done?

The body gains more energy.


What is the commercial unit of energy?

The commercial unit of energy is Kilowatt-hour.


Can energy be stored?

Yes, energy can be stored. One efficient way to store energy is in the form of chemical energy in a battery. When connected to a circuit, energy stored in the battery is released to produce electricity.
Energy can also be stored in many other ways. Batteries, gasoline, natural gas, food, water towers, a wound-up alarm clock, and a Thermos flask with hot water all store energy.

Which of the following is the energy possessed by its position?

  • Kinetic Energy
  • Potential Energy
  • Mechanical Energy
  • Electrical Energy

Watch the video and solve NCERT exercise questions in the chapter Work and Energy Class 9

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