XII
V= F/M = 10/1800
v= f/m = 5/600. hence
V: v = 10/1000: 5/600 = 2: 3, the velocity of the second
vessel being 3/2 times greater than that of the first one.
3. Compound forces.
§ 34. a) If the two forces acting upon a body are parallel
and act in the same direction (2 horses drawing a carriage), the
resultant, is equal to their sum; but if they act in opposite
directions, the resultant is equal to their difference; thus, when
ever the opposing forces are equal they destroy each other and
Equilibrium is caused.
§ 35. b) Parallelogram of forces; how the resultant of
two concurring forces may be found (the resultant being the
diagonal of the parallelogram, which may be formed by the two
concurring forces): 112.—and how also a single force may be
replaced by or decomposed into two others 113. In the same
manner the resultant of more than two concurring forces may
also be found.
If forces are represented by lines, the lines show the intensi
ty of the force (by their length) as well as their direction.
Example: A train can be moved by horses. The horses
are not allowed to go on the railway-line, but 2 horses drawing
on the right and 2 horses on the left of the railway-line produce
the same effect as 4 horses drawing in the direction of the rail
way-line. In what direction have the horses to pull? (Form
examples for all these compositions of forces.)
Applications of the Parallelogram of forces we see in a boat
or a swimmer crossing a river: 112. a kite (flight of a bird)- 114.
the wind blowing against the sails of a vessel. 113.
