If a fluid completely fills a flexible body and a pressure is applied to any external surface of that body, then the pressure is transmitted equally to all parts of the fuid. This is Pascal's principle. This is the principle behind the hydraulic press – used to press grapes, make car bodies, compress straw into bales...
To operate the press a force
is applied to the force pump which has a surface of area
in contact with the oil. This produces a pressure
The area in contact with the bale above is much larger, so a proportionately larger force is applied to the bale to compress it. If the area of the piston is
then
The applied forceis magnified by a factor