HYDROS TATIC

HYDROSTATIC branch of fluid mechanics that studies fluids at rest. It embraces the study of the conditions under which fluids are at rest in stable equilibrium; and is contrasted with fluid dynamics, the study of fluids in motion. The fundamental of Hydraulic

Hydrostatics offers physical explanations for many phenomena of everyday life, such as why atmospheric pressure changes with altitude, why wood and oil float on water, and why the surface of water is always flat and horizontal whatever the shape of its container.

HYDROSTATIC PRESSURE HYDROSTATIC PRESSURE is the pressure present within a fluid when it is at rest It acts equally in all Direction It acts a right angle to any surface in contact with the liquid Pressure

Hydraulics dealing with the mechanical properties of liquid Liquid version pf pneumatic Free surface hydraulics the branch of hydraulics dealing with free surface flow, such as occurring in rivers, canals, lakes, estuariesand seas. Its sub-field open channel flow studies the flow in open channels.

Hydrostatic Pressure Hydrostatic pressure is the weight per unit area p h =  g A D / A p h =  g D Holds for  = constant Often p h = -  g z (z+ up) D p h =  g D

Let, D = 100 m &  = 1025 kg m -3 Hydrostatic Pressure, p h =  g D = (1025 kg m -3 ) (9.8 m s -2 ) (100 m) = 1,004,500 kg m -1 s -2 [=N/m 2 ] Hydrostatic Pressure Example

p h = 1,004,500 N m -2 1 N m -2 = 1 Pascal pressure 10 5 Pa = 1 bar = 10 db p h = 1,004,500 Pa (10 db/10 5 Pa) = db Example Cont. (or unit hell)

First, 100 m depth gave a p h = db Rule of thumb: 1 db pressure ~ 1 m depth 1 db ~ 1m

Total pressure = hydrostatic + atmospheric p t = p h + p a p a varies from 950 to 1050 mb ( db) p a = p h m) Mass atmosphere = mass top 10 m ocean Total Pressure

Dealing with Stratification Density is a f(depth) Taking a layer approach dp =  (z) g dz dz = layer thickness [m] Summing over D p h =   (z) g dz (where  over depth, D) D

Example with Stratification  1 = 1025 kg m -3  2 = increases from 1025 to 1026 kg m -3 What is p h (100m)??

Example with Stratification Sum over the top 2 layers p h (100 m) = p h (layer 1) + p h (layer 2) Layer 1: p h (1) = (1025 kg m -3 ) (9.8 m s -2 ) (50 m) = 502,250 N m -2 (or Pa) 10 5 Pa = 10 db p h (1) = db

Example with Stratification Layer 2: Trick: Use average density!! p h (2) = ( kg m -3 ) (9.8 m s -2 ) (50 m) = 502,500 Pa = db Sum over top 2 layers p h (100 m) = p h (1) + p h (2) = = db

Hydrostatic Pressure Hydrostatic relationship: p h =  g D Links water properties (  ) to pressure Given  (z), we can calculate p h Proved that 1 db ~ 1 m depth Showed the atmospheric pressure is small part of the total seen at depth