What is Work?
We often use the word “work” in our daily life. For example, we will say that getting good grades in school takes a lot of “work”. In physics, the term “work” has a special meaning.
Work, in physics, occurs when a force is applied to an object to move it a distance from the starting point (also called displacement). Work is calculated as force multiplied by distance. The following equation is used to describe the job:
Work = Force * distance
or
W = Fd
How to Measure Work
The standard unit of work is the joule (J). Joule is like a newton meter where newton is force and meter is distance.
Force and Displacement
The distance (or displacement) in the work is the distance between the starting point and the ending point. The amount of travel between the two doesn’t matter. For example, if you lift a heavy object off the ground and then put it back on the ground, the distance (or displacement) is zero.
Don’t be Tricked
Measurement work can sometimes be complicated. For the equation W=Fd to work, the force used in the equation must be the force used to cause displacement or distance. Also, keep in mind that for the work to happen, the object must be moved by force. Otherwise, the distance, or “d”, in the formula is 0 and the work will be 0.
Here are some examples:
If someone pushes against the wall with all their might, but the wall doesn’t move, then no work happens. This is because the distance is zero.
If someone used force to hold a rock overhead while walking east through a field, nothing would happen. This is because the force is not in the same direction (upward force) as the distance the rock travels (eastward).
If you do a full push-up, lifting and then lowering, the total is zero. Indeed, the sum of the distances between the start and end points is zero.
If you drop your pencil, then the job is done. This is because the displacement of the pencil from your hand to the ground is greater than zero and is in the same direction as the force acting on the pencil, which is gravity.
Example problem:
A baseball player throws a ball with a force of 10 N. The ball travels 20 meters. What is the total work?
W = F * distance
W = 10N* 20 meters
W = 200 joules
More Complicated Problems
When the angle between force and displacement is not 0 degrees or 90 degrees, a more complex working formula is used. This formula includes the angle theta (Θ) as the angle between force and displacement.
W = F * d * cos Θ
In case the force and displacement are completely in the same direction then theta = 0 and cos Θ = 1. In the case of no force acting on displacement and theta = 90 degrees then cos Θ = 0 and, therefore, work = 0 .
Interesting Facts about Work
Work is a scalar quantity, not a vector quantity. This means that, unlike force and speed, it has no direction, only magnitude.
Another unit of work is the foot-pound. One foot-pound equals 1.35581795 joules.
The joule is also used as a standard unit for measuring energy.