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Last Updated : 02 Apr, 2024
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Energy in Physics is defined as the capacity of a body to do work. It is the capacity to complete a work. Energy can be broadly categorized into two categories, Kinetic Energy and Potential Energy. The capacity of an object to do the work is called the Energy. In this article, we will learn about, Energy, Types, of Energy, the Law of conservation of Energy, and others in detail.

Before learning about energy, we must first learn about, Work Done, so let’s start with the same.

What is Work?

Work done is defined as the product of the magnitude of the force acting on the body and the displacement of the body in the direction of the force. The formula of work done on a body is, 

W = F.s


  • W is the Work Done
  • F is the Force Applied
  • s is the Displacement of Object

Sign Conventions for Work Done

  • Positive work is done when both the force and the displacement are in a similar direction.

          W = F × s

  • Work done is negative when a force acts in a direction opposite to the direction of displacement.

           W = − F × s

           The angle between force and displacement is 180°.

  • Work done will be following if force and displacement are inclined at an angle less than 180°:

           W = F.s.cosθ

  • If force and displacement act at an angle of 90°, then work done is zero. The work done is 0 if a force acting on a body causes no displacement. For example, pushing a wall.

Unit of Work Done

  • Unit of work done is Joule.

One Joule is equal to Newton.Meter. 1 Joule work is said to be done when 1 Newton force is applied on an object, and the object is displaced by 1 m.

Dimensional Formula of Work Done

  • Dimensional formula of work is, [ML2T-2]

What Is Energy?

In Physics capability of a body to perform work is defined as Energy. Its unit is similar to that of work. SI unit of work or energy is Joule (Nm). Different forms of energy include, Light Energy, Heat Energy, Chemical Energy, Electrical Energy, Mechanical Energy, etc.

In simple we can say that, Energy is the ability of an object to do work. For Earth, the Sun is considered to be the ultimate source of the energy.

Units of Energy

The SI unit of energy is the Joule. It is named after James Prescott Joule. One joule is defined as the work done by the object when the force applied is 1 Newton and the displacement of the body is 1 m. Other units of energy include Calories, Kilowatt-Hours, Ergs, etc.

Dimensional Formula of Energy

As, the unit of work done and energy is the same. So, the dimensional formula for wor done and energy is the same. The dimensional formula for energy is, [ML2T-2]

Energy Conversion: Transfer and Transform

It is a well-known fact that energy can be transformed from one form to another form. The transfer of energy from one form to other form is known as energy transfer. The transformation of energy generally categorised into four ways,

  • Mechanical Energy Conversion
  • Electrical Enegy Conversion
  • Energy Conversion By Radiation
  • Energy Conversion By Heating

Law of Conservation of Energy

Law of Conservation of Energy states that, “Energy can neither be created and nor be destroyed, and it can only change its form from one form to another.” In other word we can also say that,

“In a closed and isolated system the total energy of the system is always conserved.”

This is one of the basic law of the physics and help us to explain various astronomical and physical phenomenon.

Different Types of Energy

There are various types of energy but they all can be fit into two main categories that are,

  1. Kinetic Energy (K.E)
  2. Potential Energy (P.E)


Let’e learn about them in detail.

Kinetic Energy

Objects in motion have their own energy and are able to do work. This energy is called Kinetic Energy. The Kinetic Energy (K.E.) of an object increases with the increase in the speed of the object. The kinetic energy of an object is the half of the product of the mass of the object with the square of its velocity. So in order to increase the KE of the object we have to increase the mass of the object or increase its velocity.

Kinetic Energy Formula

Suppose an object of mass ‘m’ moves with a velocity of ‘v’ then the formula use to calculate the kinetic energy of the object is,

KE = 1/2mv2

Units of Kinetic Energy

  • SI unit of K.E. is Joule which is equal to 1 kg.m2.s-2.
  • CGS unit of K.E. is erg.

Derivation of Kinetic Energy Formula

Work done, W = F × s …(i)

Due to force, the velocity changes to v, and the acceleration produced is a relation between v, u, a, and s = v2−u2 = 2as

s = (v2 – u2)/2a…(ii)

F = ma …(iii)

Substitute (ii) and (iii) in (i) we get

W = F × s

W = ma × (v2 – u2)/2a

W = 1/2m(v2 – u2)

If u = 0 (object starts at rest)

W = 1/2 mv2

Work done = Change in kinetic energy

Ek = 1/2mv2

This is the formula for the kinetic energy of an objrct.

Different Types of Kinetic Energy

Radiant Energy

The energy of wave and particles is called the radiant energy. This type of energy does not require any medium to propagate. The energy of Sun that reaches to us is an example of Radiant Energy.

Sound Energy

The energy of sound wave is called the sound energy. This is the energy of the sound and the vibrtration in the surrounding matter. This form of energy helps human to hear.

Electrical Energy

The energy of flowing elctrons are called the electrical energy. This energy is used to power all the electric appliance in our house.

Thermal Energy

Thermal energy is form of energy that is related to heat or warmth. Thermal energy works on molecular level. Geothermal energy is the form of the thermal energy, etc.

Potential Energy

When the work is done on a body, energy gets stored in the body this energy is called the Potential Energy of the body. The potential energy of an object depends on the position of the object. For example, a stretched rubber band has the elastic potential energy and this is the form potential energy.

Potential Energy Formula

The energy of an object deu to its position is called the potential energy of the object. Suppose an object of mass ‘m’ is placed at height ‘h’ against the gravitational acceleration ‘g’ then the work done is equal to the gain in potential energy of the object. Then the potential energy formula for the same is,

PE = m.g.h

Units of Potential Energy(PE)

Unit of KE and PE are both same.

  • SI unit of P.E. is Joule which is equal to 1 kg.m2.s-2.
  • In CGS system unit of P.E. is erg.

Types of Potential Energy

Variou types of potential energy includes,

  • Gravitational Potential Energy
  • Elastic Potential Energy
  • Electric Potential Energy
  • Chemical Potential Energy

Gravitational Potential Energy

Gravitational Potential Energy of an object is the potential energy of an object because its height. For example a book place at ground has less potential energy as compared to a book place at the top of a table.

Electric Potential Energy

Energy across the end of an electric circuit is an example of electric potential energy. It is caused by the negative and positive charges.

Chemical Potential Energy

Potential energy of an object due to its chemical composition is called the chemical potential energy. For example the energy of the electrochemical cell.

Elastic Potential Energy

The potential energy of an object due to stretching is called the elastic potential energy. For example the energy of stretched rubberband.

Also Check, Difference between Gravitational Potential Energy and Elastic Potential Energy

Work-Energy Theorem

Work Energy theorem states that, the change in kinetic energy on an object is equal to the work done by the object.

⇒ Wnet = (KE)final – (KE)initial

Wnet = 1/2m(v2 – u2)

In other words we can say that, the work done by the object is equal to change in kinetic energy of the object.

Mechanical Energy

The total energy of an object, i.e. the sum of kinetic energy and the potential energy is called the mechanical energy of the object.

Mechanically Energy Formula

Suppose an object of mass ‘m’ moves with a velocity ‘v’ then, the mechanical energy of the object is given by the formula,

ME = 1/2mv2 + mgh

What is Power?

Power is the rate of doing work or the rate of transfer of energy. It is denoted by P. In other the the ratio of the work done by the object by the time taken is defined as the power of the object.

P = W/t

  • SI unit is Watt (Js−1).
  • Commercial unit of power is kWh, i.e., energy used in 1 hour at 1000 Joules/second.

1kWh = 3.6×106 J

Also Check, Difference between Kinetic Energy and Potential Energy

Examples on Energy Formula

Example 1: How much work is required to stop the car in 30 s if the kinetic energy of the car is 6000 J and what is its power?


Work done to stop car = change in Kinetic energy

W = KE at stop – KE at start

W = 0 – 6000

W = -6000 J (negative sign means work is done against car)

  • Time = 30 sec (given)

Power = Work Done /Time = 6000/30 = 200 Watt

Example 2: Two passengers of mass 40 kg each sit in the car then find the Kinetic energy of car if the mass of the car is 700 kg and velocity of the car is 18 km/h.



  • Mass of Car = 700 kg
  • Mass of Each Person = 40 kg
  • Total Mass(m) = 700 + 40 + 40 = 780 kg
  • Velocity = 18 kn/hr = 18(5/18) = 5 m/s

KE = 1/2 mv2

KE = 1/2(780)(5)2

KE = 9750 J

Example 3: Find the work done by the 10 N force acting on the object at the angle of 60°, which displaces the object 10 m.



  • F = 10 N
  • s = 10 m
  • θ = 60°

W= F.s.cosθ

cos 60° = 1/2

W = (10).(10).(1/2)

W  = 50J

Example 4: 245 × 102 J of work doneto raise a 50 kg boy above the ground. How high would he be raised? (g = 9.8 m.s-2)



  • Work Done = 24500 J
  • m = 50 kg
  • g = 9.8 m.s-2

Work Done = mgh

245 × 102 = 50 × 9.8 × h

 h = 50 m

The height at which the boy is raised is 50 m.

Energy- FAQs

1. How do you Define Energy?

The capacity of an object to do work is called the energy of an object.

2. What are Types of Energy?

Generally Energy can be classified into two categories broadly,

  • Kinetic Energy(KE)
  • Potential Energy(PE)

3. Why do we get Instant Energy from Glucose?

Glucose is easily absorbed by blood as it is the simplest form of sugar. Therefore, we get instant energy from glucose.

4. What is Commercial unit of energy?

The commercial unit of energy is Kilowatt-hour (kWh)

5. What is Solar Energy?

Solar energy is a renewable form of energy. It is the energy obtained from the sun and then converted into power and electrical energy for the use of common people.

6. What is Geothermal Energy?

Geothermal energy is the energy in which the heat within the earth is converted into different forms of energy. It can further be used for cooking, bathing, electrical power generation, etc.

7. What is Nuclear Energy?

Nuclear energy, in simple words, is the energy present inside the nucleus. The energy is emitted during a nuclear reaction.

8. What is Law of Conservation of Energy?

Law of Conservation of Energy states that, energy can neither be created now be destroyed, it can only change its form from one form to another.

9. What is the 4 Types of the Energy?

The 4 types of the energy are,

  • Potential Energy
  • Kinetic Energy
  • Chemical Energy
  • Nuclear Energy

Apart form these there are various other types of the energy.

10. What is the SI unit of Energy?

The Energy is defined as the amount of workdone by an object and the SI unit of the energy is, Joule(J)

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