Fig. 18.—The force increases with the depth.
If now a cubic centimeter of water be poured upon AB it will raise the level 1 cm., or the head of water exerting pressure upon CD becomes 11 cm., or the total force in CD is 16×11 g., i.e., each square centimeter of CD receives an additional force of 1 g. Hence the force exerted on a unit area at AB is transmitted to every unit area within the vessel.
The usual form in which this law is expressed is as follows: Pressure applied to any part of a confined liquid is transmitted unchanged, in all directions, and adds the same force to all equal surfaces in contact with the liquid.
Fig. 19.—The force is proportional to the area.
The importance of this principle, as Pascal himself pointed out, lies in the fact that by its aid we are able to exert a great force upon a large area by applying a small force upon a small area of a confined liquid, both areas being in contact with the same liquid. Thus in Fig. 19 if the area of the surface CD is 2000 times the area of the surface AB, then 1 lb. applied to the liquid on AB will exert or sustain a force of 2000 lbs. on CD.
41. Hydraulic Press.—An important application of Pascal's principle is the hydraulic press. See Fig. 20. It is used for many purposes where great force is required, as in pressing paper or cloth, extracting oil from seeds, lifting heavy objects, etc. Many high school pupils have been seated in a hydraulic chair used by a dentist or barber. This chair is a modified hydraulic press.
