What is Work, Power, and Energy? 

After a good sleep at night, at morning you will be waking up highly energetic that means you have high energy in your body or system. With that high energy, you can do work. If you complete your work in time because of high energy present in you then you too have high power present in you. The technical depth of understanding will be followed in forthcoming definitions. 

Energy is a common term that energizes two properties that is flow of energy and storage of energy. The ability to do work is known as energy. 

Work is also a type of energy that flows as a transition from one body to another. Energy conservation principle “energy cannot be created nor be destroyed; it changes from one form to another.” If you apply your mechanical energy or muscle energy in a manual pump, it is termed as you have done work on the pump to get water. If energy is stored in the system it is termed internal energy. The various types of energy include potential energy, mechanical energy, chemical energy, electrical energy, and gravitational potential energy. If energy flows from one place to another it is termed kinetic energy, heat, and work. Neither heat nor work can exist as stored energy, they are transition energy. One form of energy that cannot be stored is termed work. 


When a force moves through a distance, a work is done. If a system undergoes a displacement or deformation under the action of pressure, the work is done on the system. Work acts in two types 

  • work supplied by the system  
  • work supplied to the system 

If we supply fuel and air to the engine, it converts it into heat and that heat energy will be directly converted and supplied as work by the engine system 

If we supply electrical energy to the rotary compressor present in the refrigerator or air conditioner, they will work, that work is absorbed by the refrigerant in the device and produces cool air or ice freezing. 

Sign Convention  

  • If work is supplied by the system, it is positive  
  • If work is supplied to the system, it is negative 
"work done in different systems"

Work = pressure x displacement volume  

Pressure is measured in newton/m2 

Work is measured in joule (j) 


The ability to do work is termed as energy. The energy is present in different form in nature. The unit of measurement for energy is joule (J). Energy is found in different object in different manner. 

  Different forms of energy   

 The energy conserve in the atmosphere varies of different types, we will discuss about some of the important energies. 

  • Potential energy 
  • Kinetic energy 
  • Heat energy 
  • Friction energy 
  • Enthalpy 
  • Entropy 
  • Elastic energy 
  • Stress energy 
  • Gravitational potential energy 
  • Ionization energy 
  • Magnetic energy 
  • Radiant energy 
  • Nuclear energy 
  • Elastic energy 

Potential Energy 

The energy that is stored inside the body. The potential of the body depends upon its mass. If a body is said be at rest, the energy stored inside the body is known as potential energy. 

It is denoted by equation P.E = mgz 

m- mass 

g – acceleration due to gravity 

z – datum height 

Kinetic Energy 

This energy is obtained by an object or body when it is in motion. If an object is started to move from its rest position, slowly its energy starts to convert from potential energy to kinetic energy. Kinetic energy is also known as constant velocity energy. The velocity decides the kinetic energy. 

It is denoted by equation K.E = ½ mv2 

m- mass 

v- velocity 

"Potential and Kinetic Energy demo"

Heat Energy 

If energy is created due to temperature difference, if temperature is increased in a body from lower temperature to higher temperature, slowly potential energy is converted into heat energy. 

It is denoted by equation Q = MCDT 

M - mass 

C – specific energy 

DT – temperature difference 


The maximum energy that a system can possess, or a maximum energy obtained from the system is known as enthalpy 

It is denoted by h 

Unit is kJ/kg 


The unavailable energy or lowest energy, which we cannot obtain from the system is known as entropy. 

It is denoted by S 

Unit is kJ/kg-K 

Nuclear Energy 

When two radioactive atoms are bombarded, it produces two reactions, nuclear fission reaction, and nuclear fusion reaction. These reactions will produce high heat power. 


If you can finish your work in time, then it is termed as high power. If you can’t complete your work, it is coined as less power. Power can be inferred as the rate of doing work. Power doesn’t have any direction hence it is a scalar quantity. Power is measured by its founder name James watts (WATTS -W). 

Power = work / time 

p= W t = j s =Watt =W


It was also a unit for measurement of power, it is usually taken in reference for output of engines and motors. The mechanical horse power which is about 745.7 watts 


How Work, Power, and Energy related to each other? 

Imagine a man is weighing 80 kg  

His force calculation is F = m a  

Fhuman = 80 X 9.81 = 784.8 N 

He has to lift a box, a box is weighing 40 kg  

box force calculation is F = m a  

Fbox = 40 X 9.81 = 392.4 N 

Can a man, lift this box? 


Hence, he has high potential energy than box, so he can lift it  

The man lifts the box and walks for 9.81 m  

If he walks with the box, he has done some work 

The amount of work done by the human is = force x distance  

Work = weighing force x distance = 392.4 x 9.81 = 3849 J OR N-M 

If the man does this work in 45 sec, we can calculate power 

Power = work done by man / time he took 

P = 3849 / 45 = 85.5 W OR J/S. 

Hence proved. 

You would have understood by this example scenario how energy, power and work is interconnected. 

Context and Applications    

This topic is significant in the professional exams for both undergraduate and graduate 

  • B.Sc Physics 
  • M.Sc Physics 

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