CHAPTER 8
POWER
CHAPTER LEARNING OBJECTIVES
Upon completion of this chapter, you should be able to do the following:
l Define the term “power.”
l Determine horsepower ratings.
It’s all very well to talk about how much work a
person can do. The payoff is how long it takes him or
her to do it. Look at the sailor in figure 8-1. He has
lugged 3 tons of bricks up to the second deck of the new
barracks. However, it has taken him three 10-hour
days—1,800 minutes-to do the job. In raising the
6,000 pounds 15 feet, he did 90,000 foot-pounds (ft-lb)
of work. Remember, force x distance = work. Since
it took him 1,800 minutes, he has been working at
90,000 ÷ 1,800, or 50 foot-pounds of work per minute.
That’s power—the rate of doing work. Thus, power
always includes a time element. Doubtless you could do
the same amount of work in one 10-hour day, or 600
minutes. This would mean that you would work at the
rate of 90,000 ÷ 600 = 150 foot-pounds per minute.
You then would have a power value three times as much
as that of the sailor in figure 8-1.
Apply the following formula:
Figure 8-1.-Get a horse.
8-1
