Force Systems
By possessing an understanding of Newton's Laws, following these three laws
of
graphical solutions, and understanding vector algebra you can solve
most
engineering static problems. Systems of Force Systems of force acting on
objects
in equilibrium can be classified as either concurrent or
nonconcurrent and as
either coplanar or noncoplanar. This gives us four
general categories of
systems. The first category, concurrent-coplanar forces
occur when the lines of
action of all forces lie in the same plane and pass
through a common point.
Figure 1 illustrates a concurrent-coplanar force
in such that F1, F2, and W all
lie in the same plane (the paper) and all
their lines of action have point O in
common. To determine the resultant of
concurrent force systems, you can use the
Pythagorean theorem, the law of
sines, or the law of cosines as outlined in the
previous chapter.
Nonconcurrent-coplanar force is when the lines of action of
all forces lie in
the same plane but do not pass through a common point as
illustrated in
figure 2. The magnitude and direction of the resultant force can
be
determined by the rectangular component method using the first two
equations
in figure 2, and the perpendicular distance of the line of action
of R from the
axis of rotation of the body can be found using the third
equation in figure 2.
Concurrent-noncoplanar forces are when Application
the lines of action of all
forces pass through a common point and are not in
the same plane. To find the
resultant of these forces it is best to resolve
each force into components along
three axes that make angles of 90 degrees
with each other.
Nonconcurrent-noncoplanar forces are when the lines of
action of all forces do
not pass through a common point and the forces do not
all lie in the same plane.
Stress When a restrained body is subject to
external forces, there is a tendency
for the shape of the body.