Understanding Hydrostatic Pressure and Pascal's Law

Hydrostatic Pressure

Fig. 1-4. Illustration of hydrostatic pressure

Fig. 1-4. shows a number of differently shaped, connected, open containers. Because liquid seek their own level, the liquid level as shown is at the same height in each container. This occurs because pressure is developed, with in a liquid, by the weight of the liquid above. If the liquid level in any one container were to be higher than that in any of the other containers, the higher pressure at the bottom of this container would cause some liquid to flow into the container having the lower liquid level. Also, the pressure of the liquid at any level (such as line A) is the same in each containers. Pressure increases because of the weight of the fluid. The farther down from the surface, the more pressure is created. This illustrates that the volume of liquid contained in a vessel has nothing to do with the pressure at the bottom of the vessel.

Pascal's Law.
The previous paragraph has just shown what happens to fluid in open containers. When pressure is exerted on a confined liquid, the pressure is transmitted equally in all directions through the liquid, as shown in Fig. 1-5. If the hammer strikes the solid block of wood, the force is only transmitted in a straight line. But if the hammer strikes a fluid, force is transmitted in all directions. Similarly, the pressure exerted on the liquid in Fig. 1-6. is equally distributed by the liquid throughout the system. Note how the hydraulic pressure in the tubing and containers acts with equal force in all directions.

 

Fig. 1-5. Pascal's Law

Fig. 1-6. Transmission of Fluid Presser