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Work: It Isn’t What You Think

Work is defined as an applied force over a certain distance. In physics jargon, you do work by applying a constant force, F, over a distance, s, where the angle between F and s is θ and is equal to Fs cos θ. In layman’s terms, if you push a 1,000-pound hockey puck for some distance, physics says that the work you do is the component of the force you apply in the direction of travel multiplied by the distance you go.

To get a picture of the full work spectrum, you need to look across different systems of measurement. After you have the measurement units down, you can look at practical working examples, such as pushing and dragging.

Work is a scalar, not a vector. Because work is force times distance, Fs cos θ, it has the units Newton-meter in the meters-kilograms-seconds (MKS) system. Newton-meters are awkward to work with, so they have a special name — Joules. For conversion purposes, 1 Newton multiplied by 1 meter = 1 Joule, or 1J.

In the centimeter-gram-second (CGS) system, Fs cos θ has the units dyne-centimeter, which is also called the erg (a great name for a unit of work because it sounds like what you would say when pushing a heavy weight). For conversion purposes, 1 erg = 1 dyne-centimeter. What about the foot-pound-second system? In this system, work has the units foot-pound.

Ex. 56. Fill the gaps with the words from the list below. Be ready to interpret the text.

Motion, ingot, kinetic, friction, magnitude, angle, Calorie

Holding heavy objects — like, say, a set of exercise weights — up in the air seems to take a lot of work. In physics terms, however, that isn’t true. Even though holding up weights may take a lot of biological work, no physics work takes place if the weights aren’t moving. Plenty of chemistry happens as your body supplies energy to your muscles, and you may feel a strain, but if you don’t move anything, you don’t do work in physics terms.

… is a requirement of work. For example, say that you’re pushing a huge gold ingot home after you explore a cave down the street, as shown in Figure 8-1. How much work do you have to do to get it home? First, you need to find out how much force pushing the …requires.


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