Pascal was a noted French physicist who discovered
that a closed container of fluid could be used to transfer
force from one place to another or to multiply forces by
its transmission through a fluid. Pascals law may be
stated as follows: PRESSURE APPLIED ANY-
WHERE ON A CONFINED FLUID IS TRANS-
MITTED UNDIMINISHED IN EVERY DIRECTION.
THE FORCE THUS EXERTED BY THE CONFINED
FLUID ACTS AT RIGHT ANGLES TO EVERY
PORTION OF THE SURFACE OF THE CONTAINER
AND IS EQUAL UPON EQUAL AREAS. It should be
noted that Pascals law applies to fluids-both gas and
liquid. It is the use of Pascals law that makes possible
todays hydraulic and pneumatic systems.
According to Pascals law, any force applied to a
confined fluid is transmitted in all directions throughout
the fluid regardless of the shape of the container.
Consider the effect of this in the systems shown in views
A and B of figure 10-1. If there is a resistance on the
output piston (view A, piston 2) and the input piston is
pushed downward, a pressure is created through the
fluid, which acts equally at right angles to surfaces in all
parts of the container.
If the force 1 is 100 pounds and the area of input
piston 1 is 10 square inches, then the pressure in the fluid
is 10 psi ( 100 ÷ 10). It must be emphasized that this fluid
pressure cannot be created without resistance to flow,
which, in this case, is provided by the 100 pound force
acting against the top of the output piston 2. This
pressure acts on piston 2 so that for each square inch of
its area it is pushed upward with a force of 10 pounds.
In this case, a fluid column of uniform cross section is
considered so that the area of the output piston 2 is the
same as the input piston 1, or 10 square inches;
therefore, the upward force on the output piston 2 is 100
pounds-the same as was applied to the input piston 1.
All that has been accomplished in this system was to
transmit the 100-pound force around a bend; however,
this principle underlies practically all mechanical
applications of fluid power.
At this point, it should be noted that since Pascals
law is independent of the shape of the container, it is not
necessary that the tube connecting the two pistons
should be the full area of the pistons. A connection of
any size, shape, or length will do so long as an
unobstructed passage is provided. Therefore, the system
shown in view B of figure 10-1 (a relatively small, bent
pipe connects two cylinders) will act exactly the same
as that shown in view A.
Multiplication of Forces
In figure 10-1, views A and B, the systems contain
pistons of equal area wherein the output force is equal
to the input force. Consider the situation in figure 10-2
where the input piston is much smaller than the output
piston. Assume that the area of the input piston 1 is 2
Figure 10-1.-Force transmitted from piston to piston.
Figure 10-2.-Multiplication of force.