First Principles - Sustainable Design: The Science of Sustainability and Green Engineering - page 56

Figure 2.5 Moment about a
single force.

F

F

θ

Line of action of force

A

r

d

MORE ABOUT FORCES

Force is crucial to green engineering. An integrated design strategy must account
for all forces. So let us consider briefly the various types of forces. A point force
(or concentrated force) is a vector with magnitude, direction, and location. The
force's line of action is the line in the direction of force that is extended forward
and backward.
Another aspect of force is the moment , which is the tendency of a force to
rotate, twist, or turn a rigid body around a pivot. In other words, when a body
is acted on by a moment, the body will rotate. But even if the body does not
actually rotate because it is being restrained, the moment still exists. So the units
of a moment are length m). The moment is zero when the line

of action of the force passes through the center of rotation (pivot). A moment
important to green engineering is the moment of force about a line. A pump,
for example, has a fixed rotational axis. This means that it turns around a line,
not about a pivot. The moment about a single force in shown in Figure 2.5. The
moment M of a force F about point A in the figure is the product of the force
and the perpendicular distance d from that point to the line of action for the
force. So the magnitude of this moment is

× force (e.g., N ·

M A = Fd (2.8)

Sidebar: Applying the Synthovation/Regenerative Model:
Beyond Waldon Pond

As to methods there may be a million and then some, but principles
are few. The man who grasps principles can successfully select his own
methods. The man who tries methods, ignoring principles, is sure to
have troubles.

Ralph Waldo Emerson