Introduction
Work is a common term in the society. However, the definition of work that is generally accepted in society conflicts with the definition of work suggested by Physics. A person sitting on his chair studied for entire 3 hours. He used his energy in doing the task therefore the general society considers it as work done. However, physics boldly states that there is no work done in that case. It is because work is said to be done when a force is applied on an object and the object covers some displacement in the direction of the applied force. In our condition, the person did not cover any displacement. As a result, no work was done.
The SI unit of Work is Joule (J). In terms of fundamental physical quantities, it can be written as $\text{kgm}^2\text{s}^{-2}$. The dimensions of Work is $\text{[ML}^2\text{T}^{-2}\text{]}$.
Conditions of Work Done
From the above explanation, it can be noted that work is said to be done on an object by a force if all of the following conditions are satisfied:
- Force is applied to the object
- Some displacement is covered by the object in the direction of the applied force
Types of Work Done
Work is also defined as the scalar product of force (F) and displacement (d). Thus, $$\text{Work = }\vec{F}.\vec{d} \text{ = Fd }\cos \theta$$ where $\theta$ is the angle between the line of force and displacement. Depending upon the value of $\theta$, work done can be positive, negative, or zero.
- Case I: When $0^0 \leq \ \theta < \ 90^o$, work done is said to be positive as $\cos \theta \in (0, 1]$ in the given arguments of $\theta$.
- Case II: When $\theta = 90^o$, work done is said to be zero as $\cos \theta = 0$ in the given argument of $\theta$.
- Case III: When $90^o < \theta \leq 180^o$, work done is said to be negative as $\cos \theta \in [-1, 0)$ in the given arguments of $\theta$.