Work and Energy

What Do Work and Energy State for?

In physics, the concept of work and energy is thoroughly correlated and linked to force. It is because whenever force is applied to any object, there is some work done and also some change in the energy. Work is a physical activity that includes movement in the direction of applied force. 

When is Said to be Work Done?

Work is said to be done when we apply a force which causes a movement in an object through a distance. According to physics definition, work defines itself only when an object is lifted or moved. However, it is not about an object in a stationary position. 

  • Work has only magnitude, and thus it is a scalar quantity. 

  • The SI unit of work is given by J (Joule) or Newton-meter.

The amount of work done is equal to the product of the acceleration due to gravity, the actual mass of the object, and the height with which it has travelled. Generally, the work done against gravity is represented by the following equation:

W = m*g*h

Here, m= mass of an object

g= acceleration due to gravity

W= work done

h= height through which the object is raised 

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The above diagram shows the two work sorts, namely; positive and negative. When the direction of the force applied is the same in which the object is displaced, then the work done is positive. When the applied force displaces the object in the opposite direction then the work done is said to be negative. 

Example of Work Done

When an individual kicks a ball, they are exerting an external force. Due to this external force, say F, the ball moves to some distance. The distance, with which a ball move from its rest position to another position, refers to displacement, say d. Hence, work is said to be done, and its equation is given by:

Work = Force * Displacement or

W= F * d

The equation of the work states that work done is the product of applied force and displacement.


What is Energy?

Energy refers to the ability of an individual to do work. It can be either absorbed or destroyed and can transform from one object to another. The two general forms of energy are potential energy and kinetic energy. The most common way to measure energy is to measure the amount of work done or the ability of an individual to do work.

The kinetic energy is given by the formula:

K.E. = 1/2 * m * v2

P.E. = m * g * h

Different types of energy are:

  • Elastic energy

  • Magnetic energy

  • Electrical energy

  • Heat energy

  • Mechanical energy

  • Nuclear energy

  • Chemical energy

  • Radiant energy

  • Ionization energy

  • Gravitational energy

  • Thermal energy

The unit of the energy is given by Joule (J). It is the same as that of work.

Like work, energy also has magnitude but no direction. Thus,  energy is said to be a scalar quantity.

What is the Work-energy Principle?

According to the principle of work and energy, the change in the kinetic energy of a body is directly proportional to or equivalent to the total work done on the body. The work-energy principle can be represented as:

Work was done = Final Kinetic Energy- Initial Kinetic Energy or

W = Kf – Ki

The work-energy principle is derivable from the physics law, that is, conservation law of energy. 

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The diagram shows a man applying force to move the box in the upward direction. In this case, the man's kinetic energy is equivalent to the amount of work done in moving the box. 

What is the Difference Between Work and Energy?

  • Though work and energy are scalar quantities and measured in Newton-meter or Joules, still there are some significant points of difference:

  • Whenever an applied force changes the object's distance, it is said to be work done on an object. However, the ability to create or produce some work refers to energy.

  • There is no further work; however, there are different types of energy, like sound energy, mechanical energy, and many more.

Work is said to be accomplished only if there is some displacement of the object. In case there is no displacement, but the force is applied, then the work done is zero. However, energy does not depend on whether some displacement is or not. For example, a man pushing a wall is applying force to move to a certain distance. The wall does not move, and hence the work done comes out to be zero. However, the energy of the man is released while pushing a wall.

FAQ (Frequently Asked Questions)

1. Are the Two Quantities Work and Energy the Same?

We define work as the movement in the direction of the force applied. However, energy is the ability of a person to do the work. To do work, you must possess energy. Or, in other terms, energy is the currency of doing work. If you apply some additional force to the moving object, then work done on it will give rise to its kinetic energy. 

2. What Energy Does the Falling Water Possess?

The movement of water in the dam is from a high level to a low level. The hydroelectric dam will store water inside, and hence falling water has stored gravitational potential energy from it. As water will fall from top-level to the low level, this potential energy converts to kinetic energy. Hence it will turn the turbines one which generates electricity. In this way, electricity is produced by the dam.