PARALLEL FORCES

493

Parallel Forces and Principle of Moments.
Example.—Two men A and B are carrying a 10-gallon drum of
fresh water on a 6-ft. pole supported on their shoulders. The drum
is 2 feet from A's shoulder and 4 feet from B's. The drum alone weighs
5 Ibs., what load is each man suppoitmg?
T

Fig. 9
One gallon F.W.=10 Ibs. Total weight of 10 gallons of water
and drum is therefore 105 Ibs..
If the weight were suspended at the middle of the pole (at 3 feet) the
weight would be divided equally between the two men in the proportion
as 3 is to 3, the distance of their shoulders from the weight, but the
weight is nearer to A than to B so, obviously, A's exertion must be
the greater as the forces are balanced, otherwise, something would
happen. The exertion is in inverse ratio to the length of the arm of the
lever.
Weight borne by A ___ distance of B from weight     4=      2
Weight borne by B     distance of A from weight """ 2 ~~ 1
The exertion of A is twice that of B. Divide the weight into three
parts of 35 Ibs. each.
Answer.—B carries 35 Ibs,; A carries 70 Ibs.
.
Fig. 10.
We might have applied the principle of moments to this example,
using A*s shoulder as a fulcrum, to find the load carried by B.