What is Energy?- Definition, Units, Examples, Forms, Conservation & Future

We all use energy in our daily life, or we can say energy is what makes life possible on Earth.

It is impossible for us to imagine life without energy. Whether we are moving from one place to another or are just sitting, we all have some form of energy.

In this post, I am going to share everything you need to know about energy covering its definition, units, examples, forms & what the future of energy looks like.

Let’s dive right in.

What is Energy?

Energy is something that we need to do any kind of physical activity. In physics, it is defined as: 

the capability of a system to perform work.

Energy cannot be stored, it goes continuously from one form to another. 

For example, an electric motor converts electricity into mechanical work. The electric motor does not store any kind of electrical energy.

Let’s take a more common example.

Suppose you’re running, so what happens when you run?

Of course, some work is done & the temperature of your body goes up & your body starts to sweat. 

Well in this way, you are converting the energy that you have got from food into thermal energy (in form of heat).

Also, when your foot hits the ground some kind of sound also produces, which means the energy of your body is also converted into sound.

Thus, we can say the total amount of energy remains the same & only its transfer takes place.

I hope you get to know a bit about how energy works.

Let’s have a look at its different units.


Units of Energy

The basic unit of energy is Joule (J) which is also known as the SI (International System) unit of energy.

Energy per unit time is known as power and it is expressed in Watts (W).

1 W = 1 J/s

The power represents the rate at which energy is converted or transferred. Some other units of power are Horsepower (hp), Kilowatts (kW), Megawatts (MW) & Gigawatts (GW).

  • 1 Kw = 1000 watts
  • 745.7 watts = 1 hp
  • 1 MW = 1000000 watts
  • 1 GW = 1000000000 watts

Other units of power include decibel-milliwatts, calories per second & BTU (British Thermal Unit).

Types of Energy

We all know many types of energy like mechanical, electrical, sound & light energy.

But do you know there are only two main types of energies & all others are part of them?

Here are the two:

i). Kinetic Energy

ii). Potential Energy

If you are in a hurry then you can also have a look at the below infographic from Steamism.

Source: Steamism.com

Kinetic Energy

The energy of a system due to its motion is known as kinetic energy. 

Examples of kinetic energy include walking, running, cycling, etc.

It can be calculated using the formulae given below:

Kinetic Energy Formula

where m = mass of the object & v = velocity at which it is moving.

Since kinetic energy is directly proportional to mass & velocity. So, we can say that an object having more mass & velocity will have higher kinetic energy.

Example: An airplane has higher kinetic energy compared to a car.

The various forms of kinetic energy include:

  • Mechanical Energy
  • Electrical Energy
  • Thermal Energy
  • Radiant Energy &
  • Sound Energy

Later, in the forms of energy section, I will discuss all of the above.

Potential Energy

The energy of a system due to its position is known as potential energy.

I think it’s a bit difficult to understand it just by definition. So let’s take an example of a rubber band.

When a rubber band is stretched it gains some energy which is called elastic potential energy

And when we release it, the rubber band gains kinetic energy & returns to its original shape.

The potential energy of an object can be calculated as:

P.E. = m x g x h

where m = mass of the object (in kg)

              g = acceleration due to gravity (= 9.8 m/s2 for earth)

              h = height in meters (from the surface)

As you can see, the potential energy is directly proportional to mass & height. 

So we can say that an object having higher mass & greater height will have higher potential energy.

The four main forms of potential energy are:

  • Chemical energy
  • Nuclear Energy
  • Gravitational Energy
  • Elastic Energy

All the energy forms with suitable examples are given below.

Forms of Energy

Here are some of the major forms of energy:

Kinetic Energies

1. Mechanical Energy

The energy of an object is due to its motion or rest. It is the sum of both kinetic & rest energy & can be considered a form of both kinetic or potential energy.

2. Electrical Energy

The energy that results in the movement of charged particles is known as electrical energy.

All the matter around the world is made up of a large number of tiny particles called atoms. 

And, if we go a little deep, we will find that these atoms are composed of even smaller particles called electrons, protons & neutrons.

The movement of these electrons gives rise to electrical energy.

3. Thermal Energy

The energy that comes from the temperature of matter is known as thermal energy. It is also known as heat energy.

When the temperature rises, the particles inside the matter vibrate which gives rise to a form of kinetic energy called thermal energy.

A common example of the transfer of thermal energy is the mixing of hot and cold water which results in a change in heat. The hot water becomes a little cooler as the transfer of thermal energy from hot water to cold water takes place.

4. Radiant Energy

The energy that transfers from one medium to another in the form of radiation or electromagnetic waves is known as radiant energy.

The energy transferred from the sun to the surface of the earth comes in the form of radiation & thus is the perfect example of radiant energy.

5. Sound Energy:

The energy that is produced by the vibration of objects is called sound energy.

Whatever we hear is because of the transfer of sound energy from the object that is producing it to our ears.


Potential Energies

6. Chemical Energy

Chemical compounds are made when one or more atoms are bonded with each other using a specific bond. 

The energy stored in these bonds or atoms of a compound is known as chemical energy & it releases whenever a chemical reaction takes place.

For example, substances like coal consist of chemical energy & when it burns it converts its chemical energy into heat (thermal) & light (radiant) energy.

7. Nuclear Energy

The energy that is released during nuclear fission or fusion is known as nuclear energy.

Nuclear fission is the process of splitting large atoms (such as Uranium) into smaller atoms while nuclear fusion is the process of the combination of two or smaller atoms so as to form bigger atoms.

In both these processes, there is a release of a significant amount of energy, known as nuclear energy.

8. Gravitational Energy

Gravitational energy is the energy stored in an object because of its height from the surface of the earth.

We can also say that it is associated with gravity ( force between two objects having mass).

Example: An apple falling down from a tree.

9. Elastic Energy

According to Wikipedia, elastic potential energy is the energy stored in the configuration of a material when it is subjected to elastic deformation by work performed on it.

It seems a bit difficult to understand it with the above definition. So let’s take an example.

In normal form, the spring does not have any elastic potential energy. However, when we stretch or compress it, the energy that it gains is nothing but elastic potential energy.

Conservation of Energy

According to the law of conservation of energy, the total energy of a system remains conserved (or constant).

The total energy of any system (e.g. universe) remains constant. It can neither be created nor destroyed. However, the transfer of energy from one body to another takes place.

Energy Problems & the Future

Before I talk about the future of energy across the world, let’s have a look at how we produce energy at present.

If we look at the most recent data from BP, the total energy consumption in 2018 constitutes 34% of Oil, 27% of Coal, 24% of natural gas & 4% of nuclear power.

All these are non-renewable sources & the total energy consumption based on non-renewable resources is 89%. The remaining 11% comes from renewable resources like hydro, wind & solar energy

Related: Renewable vs Non-renewable Resources


It clearly shows that a major part of our energy consumption comes from non-renewable resources.

Then, is it okay or we are using too much??

Well, according to a study by Stanford, we will run out of oil by 2052, Gas by 2060 & coal by 2090. 

So based on the above resources, we can say that, if we kept using fossil fuels at the same rate as we are currently using, then we will have nothing left until 2090.

Here are a few reasons why we are facing such energy problems:

  • Our living standard is increased & thus we are using more power compared to the past.
  • Big dependency on fossil fuels.
  • The demand is too high as the population is increasing day by day while the supply is constant.

Thus, the future of fossil fuels is not bright. 

Then, what’s the alternative?

Well, you might have heard about green energy sources like Solar Energy, wind energy & hydro energy.

These are all renewable energy sources & seem to be the future of energy.


In this post, I have shared the complete information regarding energy, its types, units & the future of energy resources.

We have also seen how fast the fossil fuels reserve is going down. However, the good news is we already have an alternative to that & it is green energy.

Green energy is nothing but energy that comes from the sun, air & water. If you are interested in exploring how solar energy works, then you are always welcome to read our blog.

Here are a few blogs that you can start with:

Have queries or suggestions? Leave them in the comments section below this post. 

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