Energy : The Property Of Objects

Table of Contents

Definition of EnergyEnergy ConversionTypes of EnergyFAQs

What is Energy?

Energy is essential to life and all living organisms. The sun, directly or indirectly, is the source of all the energy available on Earth. In Physics, energy is a quantitative property that must be transferred to an object in order for it to perform work. Hence, we can define energy as the strength to do any kind of physical activity. Thus, they say,

Energy is the ability to do work

Energy is a conserved quantity and the law of conservation of energy states that energy can neither be created nor destroyed but can only be converted from one form to another. The SI unit of energy is Joule.

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 and it is 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

History of Energy

  • The word energy is derived from the Greek word “energeia” which means activity, operation. This reference of energy possibly appeared for the first time in the work of Aristotle in the 4th century BC. In contrast to the modern definition, energeia was a qualitative philosophical concept, broad enough to include ideas such as happiness and pleasure.
  • In the late 17th century, Gottfried Leibniz proposed the idea of ‘vis visa’ or living force, which he defined as the product of the mass of an object and its velocity squared; he believed that total vis viva was conserved.
  • In 1807, Thomas Young used the term “energy” instead of vis viva, in its modern sense.
  • Major developments made in the 19th and 20th centuries by Gustave-Gaspard Coriolis, William Rankine, and James Prescott Joule led to the theory of conservation of energy,  which was formalized largely by William Thomson.

Energy Conversion: Transfer and Transform

The movement of energy from one location to another is known as energy transfer. There are energy transfers going on all the time – whenever a system changes there is a change in the way some or all of the energy is stored. 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 conservation of energy is one of the basic laws in physics. 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 the transformation of energy 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

Different Types of Energy

Forms of Energy Forms of Energy

Although there are many forms of energy, it is broadly categorized into kinetic energy and potential 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 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 being transferred between two objects, it’s known as heat.

Kinetic energy is determined by the given formula \(K.E=\frac{1}{2}mv^2\)

Different types of Kinetic Energy include:

1. Radiant energy

  • Radiant energy refers to 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.

2. 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 level of activity 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 are raising the temperature of the pizza. The molecules that make up the pizza are moving more quickly when the pizza is piping hot.
      • The warmth that you feel emanating from the engine is an example of thermal energy.

3. Sound Energy

      • The vibrations that reach the human ear are experienced by humans 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.

4. Electrical Energy

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

5. Mechanical Energy


      • Mechanical energy is the energy associated with the mechanical movement of objects.

Potential Energy

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

Potential energy is determined by the given formula
\(Potential\,Energy=m\times g\times h\)

Both potential energy and kinetic energy form mechanical energy.

Mechanical energy is determined by the following formula

Different types of potential energy include

    • 1. Gravitational Potential Energy

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

    • 2. Elastic Potential Energy

Elastic potential energy is energy 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.

    • 3. Chemical Potential Energy

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

    • 4. Electric Potential Energy 

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

Some of the examples of electric potential energy include:

      • 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

Recommended video on Kinetic Energy and Potential Energy

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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 in 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, a Thermos flask with hot water all stores of energy.

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

  1. Kinetic Energy
  2. Potential Energy
  3. Mechanical Energy
  4. Electrical Energy


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