Concept of Work

The term 'work' is used in everyday life for different purposes. Mostly, it is used when there is a physical activity that requires much effort.

However, in physics the term work is used in a very specified manner most especially in mechanics. Hence we will be defining and explaining the concept of work in its real physical sense.

Definition of Work

Work is said to be done when the application of force causes

the change in position or movement of the body to which it is applied. It is quite important to also note that the direction in which the body will move depend on the direction of the application of force.

Examples;

1. Work is done when you lift a load from the floor onto a plane or a table

2. Work is done when a car is pushed over a certain distance.

3. Work is done when an elastic body is stretched or compressed.

Note: No work is done when there is no movement of the body to which the force is applied. For example, when you lift a load from the floor onto your head standing on the same spot for several hours, you have done no work except when you lifted the load onto your head. 

Measurement of work

Since work is done when the application of force causes a body to move in a certain distance, work done is therefore the product of the force applied and the displacement of the body in the direction of the force.

Work = Force (F) x displacement (s)

The unit of work done is Joules (J) when the force is measured in Newton and the displacement in metres. 

When an object is lifted up vertically in a certain distance, work is done against gravity while when a body falls freely under the influence of gravity, the earth's gravitational field acts on the body.

In these instances, work is calculated as the product of the mass of the body (m), acceleration due to gravity (g) and the vertical height to which it ascends or falls (h).

Work done = m x g x h

Examples:

1. A girl of mass 30kg ascends a flight of stairs with total height 3.0m. Find the work done.

Solution:

In this case, remember that work is done against gravity.

mass, m = 30kg     acceleration due to gravity = 10m/s2        height, h = 3.0m

Work done = m x g x h

                  = 30 x 10 x 3.0

                  = 900Joules

2. A body is displaced through a certain distance x by a force of 30N. If the work done is 100J and the displacement is in the direction of force, what is the value of x?

Solution:

Force = 30N            Work done = 100J            Displacement = x

Work done = Force x displacement

         100J  = 30J x x

              x  = 100/ 30

              x  = 3.33m

Therefore, the displacement x = 3.33m.