Work Done And Energy

Work Done:

Their is difference in the way we use the term “work” in our day-to-day and the way we use it in science.

In science work is said to be done if it fulfills the below two conditions:

  • A force must be act on an object
  • The object must be displaced

“Work Done on an object is defined as the magnitude of the force multiplied by the distance moved by the object in the direction of the applied force”

The unit of work in “joule”. Mathematical expression for work-done:

Work Done = Force * Displacement
1 Joule = N-m


  • Work done on an object by a force would be “zero” if the displacement of the object is zero.
  • Work done is positive when the displacement is in the direction of force.
  • Work done is negative when the displacement is opposite to the direction of force


The energy possessed by an object is measured in terms of its capacity of doing work. The unit of energy is same as work.

Types of Energy;

Energy is available to us in different forms. The various forms include electrical energy, heat energy, chemical energy, light energy, mechanical energy(kinetic energy and potential energy).

Kinetic Energy:

“Kinetic energy of an object is the energy possessed by virtue of its motion”

The magnitude of kinetic energy is given by the following expression:

Kinetic Energy= 1/2mv2
where, m= mass of object
v= velocity of object

Potential Energy:

“The potential energy possessed by the object is the energy present in it by virtue of its position or configuration”

Suppose an object of mass “m” is raised to a height of “h” meter against the gravity then its gravitational potential energy is:

Potential Energy= mgh

Law Of Conservation of Energy:

This law states that energy can neither be created nor be destroyed but it can be transformed from one form to another. The total energy before and after the transformation always remains the same.


“It is defined as the rate of doing work or the rate of transfer of energy”

Suppose a person does “w” work in “t” second then its power is given by:

p= w/t

the unit of power is “watt”.

Commercial Unit of Energy:

The energy used in households, industries and commercial establishments are usually expressed in kilowatt-hour, which means “1 unit” is equivalent to “1 kilowatt-hour”.