When one end of a bar of solid material
is struck, for example with a hammer, the main force of the blow is
transmitted straight through the bar to the opposite end. The direction of
the blow determines the direction of the major force transmitted, and the
more rigid the bar, the less force is either lost in it, or transmitted at
angles different to the direction of the blow.
When a force is applied to the end of a column of a confined liquid (fig.
1) that force is transmitted straight through the column to its opposite
end, but also equally and undiminished - in every other direction, sideways,
downwards, and upwards. This physical behavior is defined by Pascal's Law
(fig. 2). Pascal's discovery has opened the way to the use of confined
fluids for power transmission and force multiplication. This is the basic
principle that forms the basis of design for various hydraulic equipment /
machinery.
Hydraulic systems provide a means of remotely controlling a wide range of
components by transmitting a force through a confined fluid. Most aircraft
use hydraulics in the braking systems and landing gear. Pneumatic systems
use compressible fluid, such as air, in their operation. Some aircraft
utilize pneumatic systems for their brakes, landing gear and movement of
flaps.
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