(FOM) Work Lesson
Work
What Does it Mean to Do Work?
The teens in the picture on the left are having fun playing basketball. The teen in the picture on the right is working hard studying for an exam. It's obvious who is doing work—or is it? Would it surprise you to learn that the teens who are working are the ones who are having fun playing basketball, while the teen who is studying isn't doing any work at all?
The scientific definition of work differs from its everyday meaning. Certain things we think of as hard work, such as writing an exam or carrying a heavy load on level ground, are not work as defined by a scientist. The scientific definition of work looks at the force exerted on an object and the distance the object moves. Specifically, in order to do work the force applied to an object must be in the same direction as the movement of the object and the object must move a certain distance. Therefore, if the object does not move then no matter how much force is exerted; no work has been done. Also, if a force is exerted perpendicular to the movement of the object, then no work has been done either. The teens who are playing basketball in the picture above are using force to move their bodies and the basketball, so they are doing work. The teen who is studying isn't moving anything, so she isn't doing work. Let's look at two more examples below, of work versus not work.
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Work |
Not Work |
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Calculating Work
We can mathematically solve to see how much work has been done. The equation for work is as follows:
W = F * d
From the equation of work, we see that the units used are for force and distance. Thus, in SI units, work is measured in newton-meters. A newton-meter is given the special name joule (J). This equation shows that the greater the force that is used to move an object or the farther the object is moved, the more work that is done.
You will be required to find all of the variables given in the equation. If you would like help rearranging the equation, then use the given triangle below.
Let's look at a couple of example problems:
- How much work is done on a 10-newton block that is lifted 5 meters off the ground by a pulley?
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Looking For: Work |
Solution: W = F * d
W = 10 N * 5 m
W = 50 J |
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Given: Force = 10 N Distance = 5 m |
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Equation: W = F * d
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- You did 150 joules of work lifting a 120-newton backpack. How far did you lift the backpack?
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Looking For: Distance |
Solution:
d =
d =
d = 1.25 m |
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Given: Work = 150 J Force = 120 N |
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Equation:
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Complete the practice problems below:
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