264 Chapter 10 Force and Force-Related Parameters
to rotate the object clockwise or counterclockwise. As a bookkeeping procedure, you may assign
a positive value to clockwise rotations and negative values to counterclockwise rotations or vice
versa. The overall tendency of the forces could then be determined from the final sign of the
sum of the moments. This approach is demonstrated in Example 10.5.Example 10.5 Determine the sum of the moment of the forces about pointOshown in Figure 10.13.
0.07 cos 35
5 cm
O
3 cm
2 cm
0.1 cos 35
50 N
50 N
35
100 N
■Figure 10.13 The diagram for Example 10.5.
Note that in calculating the moment of each force, the perpendicular distance between the line
of action of each force and the pointOis used. Moreover, for book keeping sake, we assigned
a positive sign to counterclockwise rotation.Example 10.6 Determine the moment of the two forces, shown in Figure 10.14, about pointsA,B,C,andD.
As you can see, the forces have equal magnitudes and act in opposite directions to one another.13.55 N#m
a^
MO 1 50 N 21 0.05 m 2 1 50 N 21 0.07 cos 35 m 2 1 100 N 21 0.1 cos 35 m 2
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