Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

7.7 Volume 181

than it does on the top surfaces of the object, as shown in Figure 7.15. Thus, the net effect of

fluid pressure distribution acting over the submerged surface of an object is the buoyancy force.

The magnitude of the buoyancy force is equal to the weight of the volume of the fluid dis-

placed. It is given by

(7.7)

whereFBis the buoyancy force (N), rrepresents the density of the fluid (kg /m

3

), andgis accel-

eration due to gravity (9.81 m/s

2

). If you were to fully submerge an object with a volumeV, as

shown in Figure 7.15, you would see that an equal volume of fluid has to be displaced

to make room for the volume of the object. In fact, you can use this principle to measure the

unknown volume of an object. This idea is demonstrated in Example 7.2. NASA astronauts also

make use of buoyancy and train underwater to prepare for the in-orbit repair of satellites.

This type of training takes place in the Underwater Neutral Buoyancy Simulator, shown in

the accompanying photograph. The changes in the apparent weight of the astronaut allows

him or her to prepare to work under near-zero-gravity (weightless) conditions.

Now that you understand the significance of volume in the analysis of engineering prob-

lems, let us look at some of the more common units in use. These units are shown in Table 7.6.

FBrVg

FB

■Figure 7.15

Buoyancy force acting

on a submerged surface.

TABLE 7.5 The Oxygen Consumption, Carbon Dioxide Production,

and Pulmonary Ventilation for a Man

Oxygen Carbon Dioxide Rate of

Level of Physical Consumption Production Breathing

Activity (ft

3

/h) (ft

3

/h) (ft

3

/h)

Exhausting effort 6.6 5.7 146

Strenuous work or sports 4.44 3.8 97

Moderate exercise 2.96 2.5 64

Mild exercise; light work 1.84 1.55 40

Standing; desk work 1.10 0.93 24

Sedentary, at ease 0.74 0.62 16

Reclining, at rest 0.3 0.56 12

Source:Copyright (c) 1991 American Society of Heating and Air-Conditioning Engineers, Inc. http://www.ashrae.org.

Reprinted by permission

Copyright 2010 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).

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