- By
**garin** - Follow User

- 181 Views
- Updated On :

Pressure. Pressure changes provide the push that drive ocean currents Key is the hydrostatic pressure Hydrostatic pressure is simply the weight of water acting on a unit area at depth Total pressure at depth will be sum of the hydrostatic & atmospheric, or p t = p h + p a.

Related searches for Pressure

Download Presentation
## PowerPoint Slideshow about 'Pressure' - garin

**An Image/Link below is provided (as is) to download presentation**

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

Pressure

- Pressure changes provide the push that drive ocean currents
- Key is the hydrostatic pressure
- Hydrostatic pressure is simply the weight of water acting on a unit area at depth
- Total pressure at depth will be sum of the hydrostatic & atmospheric, or pt = ph + pa

Hydrostatic Pressure

- Hydrostatic pressure is simply the weight of water acting on a unit area at depth
- Mass seawater in column = r A D = [kg]
- A = cross-sectional area of column [m2]
- D = depth of water column [m]

- Weight column = (r A D) * g
- Mass * acceleration gravity (g = 9.8 m s-2)

Hydrostatic Pressure

- Hydrostatic pressure is the weight per unit area
- ph = r g A D / A
ph= r g D

Holds for r = constant

Often ph= - r g z (z+ up)

D

ph = r g D

- Let, D = 100 m & r = 1025 kg m-3
- Hydrostatic Pressure, ph= r g D
= (1025 kg m-3) (9.8 m s-2) (100 m)

= 1,004,500 kg m-1 s-2 [=N/m2]

- Pressure is a stress (like tw) but normal to the surface not along it

- ph = 1,004,500 N m-2
- 1 N m-2 = 1 Pascal pressure
- 105 Pa = 1 bar = 10 db
- ph = 1,004,500 Pa (10 db/105 Pa)
= 100.45 db

- First, 100 m depth gave a ph = 100.45 db
- Rule of thumb:
1 db pressure ~ 1 m depth

- Total pressure = hydrostatic + atmospheric
pt = ph + pa

- pa varies from 950 to 1050 mb (9.5-10.5 db)
- pa = ph(@~10 m)
- Mass atmosphere = mass top 10 m ocean

Dealing with Stratification

- Density is a f(depth)
- Taking a layer approach
dp = r(z) g dz

dz = layer thickness [m]

- Summing over D
ph= S r(z) g dz (where S over depth, D)

D

Example with Stratification

r1 = 1025 kg m-3

r2 = increases from 1025 to 1026 kg m-3

What is ph(100m)??

Example with Stratification

- Sum over the top 2 layers
ph(100 m) = ph(layer 1) + ph(layer 2)

- Layer 1:
ph(1) = (1025 kg m-3) (9.8 m s-2) (50 m)

= 502,250 N m-2 (or Pa)

105 Pa = 10 db

ph(1) = 50.22 db

Example with Stratification

- Layer 2:
Trick: Use average density!!

ph(2) = (1025.5 kg m-3) (9.8 m s-2) (50 m)

= 502,500 Pa = 50.25 db

- Sum over top 2 layers
ph(100 m) = ph(1) + ph(2)

= 50.22 + 50.25 = 100.47 db

Hydrostatic Pressure

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

Download Presentation

Connecting to Server..