Pascal’s Law states that any pressure applied to a static (non-moving/flowing) liquid in a closed container will be transmitted undiminished to every part of the fluid, as well as to the walls of the container. This is the law/principle that explains how hydraulic car lifts work. Although the pressure is the same at all points in a static liquid, the force (depending on the area it is exerted over) does not necessarily stay the same. If, for example, some small force (F1) is applied over a small area (A1), a certain amount of pressure is produced (P1). This, in fact, is the definition of pressure P1 = F1/A1. Since the pressure at any other point (say P2) will be the same, if the area (A2) is larger than A1, the force produced will be large. This can easily be shown by re-arranging the formula P1 = F1/A1 into F2=P2xA2. Since P2 is the same as P1, but A2 is larger than A1, you can easily see that the force is increased.


10 N of force is applied to an area of 5 cm2
P1 = F1/A1
P1 = 10 N/5cm2
P1 = 2 N/cm2

P2, by Pascal’s Law also equals 2 N/cm2

If that pressure is applied over a larger area (A2), say 10 cm2 we can see that the force will be 20 N

F2 = P2xA2
F2 = 2 2/cm2 x 10 cm2

This can be demonstrated with a neat demo using a glass soda/beer bottle filled with water. The top of the soda/beer bottle has a small area and the bottom a larger one. If you hit the top of the bottle with the palm of your hand with sufficient force, the pressure is transferred to the water equally in all directions, and since the bottom of the  bottle has a larger area, the force you hit the top with is multiplied, and it knocks out the bottom of the bottle. Science works!

Jan 20th, 2014 – Application of Pascal’s Law