\fdO'^ - Old Forge Coal Mines

ELEMENTARY MECHANICS. 177
(417) No. It can only be counteracted by another
equal couple which tends to revolve the body in an opposite
direction.
(418)
See Art. 914.
(419) Draw the quadrilateral as shown in Fig. 29.
Divide it into two triangles by the diagonal B D. 'The
center of gravity of the triangle B C D \s found to be at a,
and the center of gravity of the triangle A B D is found to
be at d (Art. 914). Join a and d by the line a d, which, on
being measured, is found to have a length of 4. 27 inches.
From C and A drop the perpendiculars C /'' and A G on the
diagonal B D. Then, area of the triangle ABD= - (AGx
lit
B D), and area of the triangle B C D=\ {C F x B D).
Measuring these distances, B Z> = 11', C F=5.l\ and
A G= 7.7'.
Area ABD=\ x7.7xll = 42.35 sq. in.
Area BCD=\ X 5.1x11 = 28.05 sq. in.
According to formula 20, the distance of O, the center of
28.05 X 4.27
gravity, from ^ is
= 1. 7. Therefore, the cen-
^g^^^^^^ 3^
ter of gravity is on the line ^ ^ at a distance of 1.7' from b.
(420) See Fig. 30. The
center of gravity lies at the
geometrical center of the pentagon,
which may be found as
follows : From any vertex draw
a line to the middle point of the
opposite side. Repeat the
operation for any other vertex,
and the intersection of the two
lines will be the desired center
of gravity.
Fig. ao.