Water exerts pressure on immersed objects due to the weight of the fluid above, creating a pressure gradient that increases with depth. This pressure is isotropic at any given location, meaning it acts equally in all directions. The difference in pressure between the top and bottom surfaces of an object results in buoyant forces, which can cause the object to float if the upward force exceeds the downward gravitational force. Understanding these principles is crucial for applications in fluid mechanics, such as analyzing forces on structures like dams.
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Chestermiller said:It's also important to be aware that, at any given location in the fluid, the pressure is isotropic, and pushes equally in all directions.
As a PhD engineer with 45 years of fluid mechanics experience, I can assure you that it is true. Otherwise, how do you think water exerts a horizontal force on a vertical dam?dipole said:I don't think this is true. In water, for example, the force of gravity creates a pressure gradient in the water normal to the surface. This is where buoyant forces come from - the pressure is greater on the bottom surface of an object then at the top surface, and the difference in pressure creates a force which pushes it upwards. If this force is greater than the force due to gravity, it floats.
Chestermiller said:As a PhD engineer with 45 years of fluid mechanics experience, I can assure you that it is true. Otherwise, how do you think water exerts a horizontal force on a vertical dam?
So is the horizontal force of the water the same at the bottom of the vertical dam as the top?Chestermiller said:As a PhD engineer with 45 years of fluid mechanics experience, I can assure you that it is true. Otherwise, how do you think water exerts a horizontal force on a vertical dam?
No. The pressure increases with depth below the surface, so the horizontal force (on a unit area) will be greater at the bottom of the dam.Buckleymanor said:So is the horizontal force of the water the same at the bottom of the vertical dam as the top?
I am not sure what Chestermiller is saying.Doc Al said:No. The pressure increases with depth below the surface, so the horizontal force (on a unit area) will be greater at the bottom of the dam.
Fluid flow is isotropic so does this apply to the pressure difference between the top and bottom of the dam also.It's also important to be aware that, at any given location in the fluid, the pressure is isotropic, and pushes equally in all directions.
Please reread it:Buckleymanor said:I am not sure what Chestermiller is saying.
Chestermiller said:It's also important to be aware that, at any given location in the fluid, the pressure is isotropic, and pushes equally in all directions.
Doc Al said:Please reread it:
At any given location, the pressure is the same in all directions. Different locations, such as the top and bottom of the dam, can certainly have different pressures.
How can it be there must be a gradient if it's different at the top location.Doc Al said:Please reread it:
At any given location, the pressure is the same in all directions. Different locations, such as the top and bottom of the dam, can certainly have different pressures.
Buckleymanor said:How can it be there must be a gradient if it's different at the top location.
I still don't grasp it.
Probably what I do not understand is the distance being zero.jbriggs444 said:But if the distance is zero the pressure difference is zero.
Probably what I do not understand is the distance being zero.
I can not see a zero distance unless there is no substance.
Is it a theoretical construct similar to infinity but in reverse.
Thanks that makes some sense to my misunderstandings.CWatters said:Yes.
You could measure the pressure at two points of different depths. Then plot a graph of the pressure difference vs distance between the points. Extrapolate the graph towards zero separation and you will find the predicted pressure difference is also zero.
Would that make a physical difference.Chestermiller said:Buckleymanor: Would it be correct to say that you haven't had calculus yet, and thus do not understand the concept of a derivative?
Chet
No. But it would make a difference in your understanding of what a pressure gradient means, and how limits are taken as two points move very close together.Buckleymanor said:Would that make a physical difference.