Physics - Work and Energy


  • When acting (applying force), there is a displacement of the point of application in the direction of the force, is known as work.

  • The term work was first introduced by the French mathematician GaspardGustave Coriolis in 1826.

  • Work done by a force acting on the object is equal to the magnitude of the force multiplied by the distance moved in the direction of the force and it is calculated as −

  • Work done (W) = Force (F) × Displacement (s)

  • Work has the only magnitude and no direction.

  • The SI unit of work is the joule (J).


  • Energy can be converted in form, but cannot be created or destroyed. For example, producing electric energy from solar energy, etc.

  • The object which does the work loses energy and the object on which the work is done gains energy.

  • Further, the object that possesses energy can exert a force on another object to transfer energy from former to later.

  • The energy possessed by an object is therefore measured in terms of its capacity of doing work.

  • The SI unit of energy is joule (J).

Forms of Energy

  • Following are the major forms of the energy −

    • Potential energy

    • Kinetic energy

    • Heat energy

    • Chemical energy

    • Electrical energy

    • Light energy

  • Let’s discuss each one in brief

Potential Energy

  • The energy, possessed by a body by virtue of its position relative to others, is known as Potential energy.

  • So, potential energy is the stored energy in an object. For example, gravitational potential energy, elastic potential energy, electrical potential energy, etc.

  • The SI unit of potential energy is joule (J).

  • The term potential energy was introduced by Scottish engineer and physicist William Rankine.

Kinetic Energy

  • The energy that an object possesses because of its motion, is known as kinetic energy.

Kinetic Energy
  • The running/moving body maintains its kinetic energy unless its speed changes (increases or decreases).

  • The SI unit of kinetic energy is joule (J).

Heat Energy

  • Heat is a form of energy transferred spontaneously from a hotter to a colder body.

Chemical Energy

  • The potential of a chemical substance to experience a transformation through a chemical reaction and transform other chemical substances is known as chemical energy. E.g. Breaking or making of chemical bonds, batteries, etc.

  • The chemical energy of a (chemical) substance can be converted to other forms of energy by a chemical reaction. E.g., green plants convert solar energy to chemical energy (commonly of oxygen) by the process of photosynthesis.

Electrical Energy

  • The energy, derived from electric potential energy or kinetic energy, is known as electrical energy.

  • Electricity is normally produced by electromechanical generators at a power station.

  • The electromechanical generators primarily are driven by heat engines fueled by the kinetic energy of flowing water and wind.

  • The electromechanical generators are also driven by heat engines fueled by chemical combustion or nuclear fission.

Light Energy

  • Light is a form of electromagnetic radiation.

  • Light energy most likely is the only form of energy that we can really see.

Light Energy
  • Light is transferring energy through the space in a natural way. E.g. solar energy.

Law of Conservation of Energy

  • Law of conservation of energy states that energy can neither be created nor be destroyed; however, it can be only transformed from one form to another.

  • According to the law of conservation of energy, the total energy before and after the transformation remains the same.

  • The law of conservation of energy remains valid in all conditions and locations and for all kinds of transformations.