XIII
This figure illustrates what we tried to explain in Q. 113, (page 45).
The puff of the wind (c f) strikes against the sail-cloth (c d) obliquely, and
its force is decomposed into two forces, one of which (e h) acts along the
surface of the sail, thus becoming useless; while the other (g e) presses
upon the sail in a vertical direction. But on account of the oblique posi
tion of the sail the force g e or e m also cannot exert its full effect, but is
decomposed again into two others: one of these (e i) moves the vessel in
the direction of its keel, the other one (e k) pushes the vessel sideways.
As the ship is built in such a manner that the resistance of water in front
of the vessel is the least possible and sideways the greatest possible, and
as the steer helps to maintain the position of the body of the ship, it will
move forward.
§ 36. 4) An instrument for transmitting the action of a
force is called a machine and the moving force is called the
motor. By such machines the force cannot be increased, for
what apparently is gained in force, we lose in time. Although
the mechanical advantage is always equal to the mechanical loss,
we find it very often convenient to modify the action of a force
in such a way, that power is won at the expense of time.
The most simple machines are the following: 115. We distinguish bet
ween the height, base and length of such a plane.
