My question is about specific gravity of flowing water.

[Apakrat]

If one cubic foot of river water at 62.4 lbs. is moving 5 ft per second at the surface of a river is moving 312 lbs per second, is one cubic foot of river water between 9 & 10 feet below the surface moving 3120 lbs. per second???

At 74th year working on IR-One2 PhD from UHK - - -

 

[FeX32]

If you are talking lbm then no.
(I assumed I understood your phrase)



Fe

 

[Apakrat]

Thank You FeX32.

I was referring to simple 16 ounces per pound weight.

I am aware that moving "mass" is derived by converting to "slugs" or 32.174 lbs. per "slug", if this old mans understand in of Newton's thingy is correct.

At 74th year working on IR-One2 PhD from UHK - - -

 

[tkall]

Isn't this similar to: Which weighs more, a pound of feathers or a pound of lead??? A ft^3 water weighs 62.4 lbs everywhere...unless you consider decreasing gravitational attraction as a function of elevation...or the waters velocity. As it approaches C, its mass increases. Sorry...just feeling kind of punchy on a saturday morning.

 

[hydtools]

No, certainly not 10x more unless the river speed is 10x greater at 10ft depth. The velocity at 10ft below the surface may be slower than at the surface, especially if 10ft is close to the bottom. The weight per cubic foot will be the same, 62.4 lb/ft^3.

Ted

 

[FeX32]

That's kinda what I meant.
The best way to answer the question in my view would simply be to state that if the water moves at 312lbm/sec at the surface it has precisely the same 312lbm/sec 10 feet below assuming a linear and flat velocity profile.
Gravitational attraction is negligible for these purposes.
And compressibility is negligible for water.

Now if we were talking about the atmosphere 10000km up and at the surface we would come to a different conclusion.



Fe

 

[jmw]

Unless there is a temperature difference at different depths?

JMW

http://www.ViscoAnalyser.com

 

[hydtools]

Between 32F and 212F water density decreases only 4%, 2.6lb/ft^3. Density change for normal river temperature variations is negligble.
At normal pressures water is incompressible, so density at 10 feet does not change due to pressure. Although hydrostatic pressure does change directly with increasing depth to approx. 4 psi at 10 feet.

Ted

 

[JLSeagull]

Kinda makes ya wanna use SI units, huh?

 

[hydtools]

I don't know, from 0C to 100C the density still changes only 4%.

Ted

 

[cvg]

In SI units - at 0C, the river is frozen and probably not flowing. at 100C, the river is boiling. Seriously, the original question was in regards to a 3 meter deep river and temperature differential would be a few degrees celsius at worst. Therefore, SG difference would probably be negligble. In addition, the question was also related to flow velocity and SG of water does not change with respect to flow velocity within the realm of "normal" river flow velocities.

 

[IFRs]

If this were an ocean river, the salinity might vary by depth and therefore the density. For that matter, lower down there may be more silt in the water.

 

[FeX32]

The silt on the surface of Mars helps all the bit.

No really, maybe we should be talking about Mars.



Fe

 

[Apakrat]

Just gotta thank all for contributing great and useful information.

Wanna invite those interested to visit

http://www.eng-tips.com/viewthread.cfm?qid=251048

where assistance is needed involving a waterwheel question.

At 74th year working on IR-One2 - - UHK PhD - - -

 

[IRstuff]

Would certainly help if you post the correct link: thread626-251370

TTFN

FAQ731-376