Is the relationship between water pressure and gravity a direct correlation?

In summary: SmithIn summary, the relationship between water pressure and the weight of the water is direct and linear, meaning that if the weight of the water changes, the pressure will change accordingly. This can be seen when comparing the crush depth of a submersible on Earth to a watery planet with one fourth of Earth's gravity. However, there are two caveats to consider: gravitational force changes with distance from the center of a body, and water is not completely incompressible. Additionally, factors such as surface tension, friction, viscosity, and compressibility can also affect water pressure and resistance to motion in water. While water may be slightly compressible, this does not have a significant impact on water resistance in a lower gravity environment.
  • #1
Lelan Thara
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I hope this is the best sub-forum for this question:

How direct is the relationship between water pressure and the weight of the water, as determined by the local gravity where the water is?

In other words - let's say we have a submersible with a crush depth of 1000 feet on Earth. If we moved that submersible to a watery planet with one fourth of Earth's gravity - would the crush depth become 4000 feet?

To phrase it another way - if I had a body of water large enough to swim in in a microgravity environment - would the water offer any resistance as I swam through it?

Do issues of surface tension, friction, viscosity and so so on play a significant role in determining water pressure? Or is it a simple direct correlation between water pressure and gravity - half the gravity means half the water pressure for equal volumes of water?

Thanks very much.
 
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  • #2
Lelan Thara said:
How direct is the relationship between water pressure and the weight of the water, as determined by the local gravity where the water is?
Direct, linear.
In other words - let's say we have a submersible with a crush depth of 1000 feet on Earth. If we moved that submersible to a watery planet with one fourth of Earth's gravity - would the crush depth become 4000 feet?
Yep. Since the pressure is simply the weight of the column of water above the submersible, if the water weighs one fourth as much, it can go four times as deep. Two caveats:

1. Gravitational force changes with distance from the center of a body.
2. Water is not completely incompressible.

On earth, anyway, these two considerations are essentially irrelevant, but they may not be on your hypothetical other planet.
To phrase it another way - if I had a body of water large enough to swim in in a microgravity environment - would the water offer any resistance as I swam through it?

Do issues of surface tension, friction, viscosity and so so on play a significant role in determining water pressure?
Yes! (to both questions) Resistance to motion in water has nothing to do with the pressure of the water (same caveats as above, though). The resistance (and this goes for air too) is based on the density and viscosity of the fluid, and sometimes compressibility.

Surface tension, itself will only affect motion on the surface.

We may move this thread...
 
  • #3
i always wondered how pressure as a function of depth was affected by irregular containers. i keep thinking of sensible ways to calculate it that give absurd results in certain configurations
 
  • #4
Thank you, Russ. One further question about your statement below:


russ_watters said:
Yes! (to both questions) Resistance to motion in water has nothing to do with the pressure of the water (same caveats as above, though). The resistance (and this goes for air too) is based on the density and viscosity of the fluid, and sometimes compressibility.

Surface tension, itself will only affect motion on the surface.

Since water is very slightly compressible - and that compression, in a natural deep water environment, would come from the weight of the water - would I expect somewhat less water resistance in a lower gravity environment?
 
  • #5
Water is essentially incompressible, meaning that the difference in figures like "water resistance," by which I assume you mean drag, are only affected in a negligible way. You are correct, though, that the slight compressibility means that deep water is denser than shallow water, even with all other factors like temperature held constant. Denser water means, of course, more drag on a submersible vehicle. Again though, this effect is so tiny that it can be ignored, even on other planets.

- Warren
 

1. What is water pressure?

Water pressure is the force per unit area exerted by the weight of water. It is typically measured in units of pounds per square inch (psi) or pascals (Pa).

2. How does gravity affect water pressure?

Gravity plays a crucial role in determining water pressure. The force of gravity pulls the water downwards, causing it to accumulate at the bottom. As more water accumulates, the weight and pressure at the bottom increase, resulting in higher water pressure.

3. What factors can affect water pressure?

The main factors that can affect water pressure include the depth of the water, the amount of water present, and atmospheric pressure. Other factors such as temperature, salinity, and density can also play a role in determining water pressure.

4. How is water pressure measured?

Water pressure is typically measured using a pressure gauge, which consists of a small tube filled with a liquid, such as mercury or oil. The pressure of the water pushes against the liquid, causing it to rise and indicate the pressure on a scale.

5. What are some real-world applications of understanding water pressure and gravity?

Understanding water pressure and gravity is essential in many scientific fields, including hydrology, marine biology, and engineering. It is also crucial for practical applications such as plumbing, water distribution, and hydraulic systems in machinery.

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