48. The parallelogram of forces enables us to find the resultant of two
forces which intersect: but since parallel forces do not intersect, the
construction does not avail to determine the resultant of two parallel
forces. We can, however, find this resultant very simply by other means.
[Illustration: FIG. 19.]
49. Fig. 19 represents a wooden rod 4' long, sustained by resting on
two supports A and B, and having the length A B divided into 14 equal
parts. Let a weight of 14 lbs. be hung on the rod at its middle point
C; this weight must be borne by the supports, and it is evident that
they will bear the load in equal shares, for since the weight is at the
middle of the rod there is no reason why one end should be differently
circumstanced from the other. Hence the total pressure on each of the
supports will be 7 lbs., together with half the weight of the wooden
bar.
50. If the weight of 14 lbs. be placed, not at the centre of the bar,
but at some other point such as D, it is not then so easy to see in
what proportion the weight is distributed between the supports. We
can easily understand that the support near the weight must bear more
than the remote one, but how much more? When we are able to answer
this question, we shall see that it will lead us to a knowledge of the
composition of parallel forces.