How Do You Calculate Pressure and Force in Deep Sea Conditions?

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In summary, the conversation discusses a problem involving the calculation of pressure and force at a given depth in sea water. It is solved using equations such as P=pgh and P=F/A, but there is confusion over the inclusion of atmospheric pressure and the conversion of units. The conversation concludes with the correction of a calculation error and the realization that mistakes can happen.
  • #1
ceeforcynthia
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[SOLVED] Density/Sea Water Problem

Assume the density of sea water is 1024 kg/m^3 and take the atmospheric pressure equal to 101000Pa. The acceration due to gravity is 9.8m/s^2. Calculate the pressure at an ocean depth of 1260m. Answer in Pa.

Calculate the total force exerted on the outside of a circular submarine window of a diameter of 27.2cm at this depth. Answer in units of N.




p=m/v | P=F/A | P=pgh
p=density, P= pressure, F=force, A=area, g=gravity, h=height




For this problem, I used P=pgh without regard to the pascals. Then for part II, I used my pressure from the first part and plugged it into P=F/A... I used the area of the submarine window with a diameter of 27.2. Neither got me the right answer... and I'm not sure what equations to use now.
 
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  • #2
Did you add the the pressure due to the atmosphere to the pressure you calculated due to the water?
 
  • #3
No, thank you! Although I'm not sure why you would have to add the pascals... I thought the equation P=pgh already encompassed the atmospheric pressure ><
 
  • #4
The way we calculate pressure is to find the weight of whatever substance it is acting on a certain area. if you look at the expression you have it should be obvious now that it only takes into account water pressure, thus you have to add on the atmospheric pressure as well.
 
  • #5
Well that makes sense. See our teacher never explains to us these things.

However, now when I use the pressure that I got, 12644352 and plug it into P=F/A for part II, I get the wrong Newtons.
 
  • #6
What exactly are the calculations you're making?
 
  • #7
I got the area of the submarine window... (27.2cm/2)^2 and pressure: P using F=PxA.
 
  • #8
be careful of the units then because the window size is given in cm and the SI units of pressure are Newtons per meter square.

EDIT: Just noticed the window is circular. What is the area of a circle?
 
Last edited:
  • #9
I got the area to be .018496m^2 >< but it doesn't work! arghh...
 
  • #10
I get a different area. Remember that the area of a circle is [itex] \pi r^2[/itex] where [itex] r = d/2 [/itex].
 
  • #11
Oh wow, thank you so much. I hate overlooking the obvious... it's been a long week. ><
 
  • #12
No problem. We've all made the same mistakes at some point.
 

1. What is density and why is it important in sea water?

Density is a measure of how much mass is contained in a given volume of a substance. In sea water, density is important because it affects the movement and circulation of ocean currents, as well as the mixing of different layers of water in the ocean.

2. How does temperature affect the density of sea water?

As temperature increases, the density of sea water decreases. This is because warm water molecules are more energetic and therefore take up more space, causing the water to expand and become less dense. Conversely, as temperature decreases, the density of sea water increases.

3. What is the relationship between salinity and density in sea water?

Salinity, or the amount of dissolved salts in sea water, also affects its density. The higher the salinity, the more dense the water is. This is because salt molecules take up space and make the water more compact, increasing its density.

4. How does pressure change the density of sea water?

Pressure can also affect the density of sea water. As depth increases, the weight of the water above increases, compressing the water molecules and making them more dense. This is why water at the bottom of the ocean is typically denser than water at the surface.

5. How is density used to study and measure changes in the ocean?

Scientists use density measurements to study and track changes in the ocean, such as changes in temperature and salinity. By understanding how these factors affect the density of sea water, researchers can better understand and predict changes in ocean currents, climate, and marine life.

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