2016 Jan

Fundamentals of Work

January 26, 2016

Fundamentals of Work 2

Life is all about work, but what really does the term work refer to. In physics, work is defined as an activity that involves a force and movement in the direction of the force that is being exerted. S.I. units of work is the Joule where 1 Joule = 1 Newton meter. For example, when a force of 500 newton pushes an object over a distance of 10 m in the force’s direction, the work done is taken to be the product of the force and the distance moved which gives a work of 5000 joules.

Let us analyze the work that is performed by an agent that is exerting a constant force F and causing a displacement s. Note: force is a vector since it has a direction and a magnitude. Also the displacement is a vector. That is why the two are denoted as F and s in bold. The work that is done equals the product of the magnitude of the displacement and the component of F along the direction of s.

The above is illustrated in the Figure below:

Work Done

First, we will have to get the magnitude of the component of the exerted force that is in the direction of the displacement. That is the reason as to why we use the Fcos(theta). So the product will be the product of the Fcos(theta) and the displacement s. This gives: W = s Fcos(theta).

During our H2 Physics tuition classes on Work Energy Power, we raised the following points as well:

1. If the displacement s is zero, then the work, W is zero as well; meaning that there is no work done when holding a heavy box, or pushing against a wall or exerting/using force when there is no displacement attained.

2. Also, if the force F exerted is perpendicular to the displacement s then work done is zero. This for example shows that there is no work done when horizontally carrying a bucket of water.

3. Work can also be negative or positive depending on the direction of the F relative to s. The work done is greater than zero when the component of F along s is in the same direction as s , and less than zero when the component of F along s is in the opposite direction of s.

4. If force F is acting along the direction of s, work done = F s. This is because theta = 0 and cos 0 = 1.

5. Although the displacement and force are vectors, work is a scalar.

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