Just because your water volume is large this might have an effect on you math, so: 1 ft^3 of water is 62.43lbs at 32 degrees fahrenheit. Assuming that your tank will be heated between 70 and 80 degrees, you would be safe in calculating it as 62.4lbs/ft^3.
Hydrostatic Pressure Calculation (Pressure on tank walls)
- Thread starter nolapete
- Start date
Since you guys evidently DON'T get that I was using my tank as an example, let's make it simpler.
Get a gallon container.
Weigh it empty.
Weigh it full.
Subtract first number from second number
Multiply * 7.48 (approx. US gallons in a cubic foot)
There's your water weight.
Replace my 62 approximation.
I swear you guys are making this too difficult.
A couple ounces or even pounds difference in our water weights doesn't matter. If you want to be so technical, take a cubic foot of water from your own tank and weigh it to get the exact weight for your situation. It will be at the correct temperature and have the correct TDS to give you accurate numbers.
The whole purpose of this was to show how to get an APPROXIMATION of the outward pressure on any given tank surface.
Use the engineering link and the hydrostatic paradox link and come to your own conclusion.
Get a gallon container.
Weigh it empty.
Weigh it full.
Subtract first number from second number
Multiply * 7.48 (approx. US gallons in a cubic foot)
There's your water weight.
Replace my 62 approximation.
I swear you guys are making this too difficult.
A couple ounces or even pounds difference in our water weights doesn't matter. If you want to be so technical, take a cubic foot of water from your own tank and weigh it to get the exact weight for your situation. It will be at the correct temperature and have the correct TDS to give you accurate numbers.
The whole purpose of this was to show how to get an APPROXIMATION of the outward pressure on any given tank surface.
Use the engineering link and the hydrostatic paradox link and come to your own conclusion.
Nolapete. I just want to clarify. When you get the 310 pounds/ft^2, that is at the BOTTOM of your tank. So you can not use that figure to get pounds of force on the side walls since the amount of pressure exerted at a higher depth is less than a lower depth.
Also, you seem to be making this more difficult. Its much easier this way, I think. I suppose do it how you want if it works for you.
To get pressure at depth
5' / 2.31' = 2.164 PSI (Pounds per sqaure inch)
You tank bottom is 144" x 98" which equals out to be 14112 sq/in
To get weight at same depth
14112 * 2.164 = 30,538 lbs. This is at the bottom of the tank. So there is roughly 311.61 lbs per sqaure foot at the bottom of your tank.
So if you wanted to, you could say you have 30,538lbs of horixontal thrust at the base of your tank.
To get pounds per sqaure foot
14112 / 144 = 98 sq/ft
30538 / 98 = 311.61 lbs/ft^2
You can not use the PSI rating or the lbs/foot^2 at 5' for your side walls because at depth of 1 ft, there is only .432 PSI which equals out to be 62.20 lbs per sqaure foot.
To get weight at different depth and pounds per sq/ft
.432 * 14112 = 6096.38 lbs
6096.38 / 98 = 62.20 lbs/ft^2
When you get a PSI rating at a specific depth, you can only figure the total pound force AT that specific depth, not lower or higher than that specific depth.
Ounces, probably not. 1 or two more pounds per sqaure foot will make a huge difference
144*60 = 8640 sq/in
The only way you can get the total pounds of force exerted on this piece of glass is if you use this piece of glass at the bottom of your tank. Gravity pulls down, not to the side
8640 * 2.164 = 18696 lbs at the bottom.
I have looked at that link and I think you are misunderstanding it.
The author tells you that the pressure in a liquid at a point (meaning depth) is the same in all directions (360 degrees of direction) at that specific point (depth).
It doesn't matter the length of anything to get the pressure. Pressure is different than force (Chompers corrected me one day, so I shall share.) Pressure is reduced when the area gets larger. The FORCE gets greater as the area gets larger. You need PRESSURE to get FORCE.
The Hoover dam example in that link is perfect. The dame is larger at the base because there is over 18 tons of horizontal thrust.
How did the author get that? Well, he said the lake is 600 ft deep. So,
600 / 2.31 = 259.74 PSI (Thats a lot)
259.74 * 144 = 37402 lbs per sq/ft
37402 / 2000 = 18.70 tons per sqaure foot.
Horizontal thrust = 18.70 tons per sq/ft @ 600' depth
Now at a depth of 200'
200 / 2.31 = 86.58 PSI
86.58 * 144 = 12467 lbs per sq/ft
12467 / 2000 = 6.23 Tons per sq/ft.
Horizontal Thrust = 6.23 tons per sq/ft @ 200' depth
(144 is the total sqaure inches in a 12"x12" area)
(2000 is roughly the amount of pounds in 1 ton)
Lets not throw temperature into this. Otherwise, lets calculate for his altitude in as well. Above or below sea level will change how much water weighs. Don't ask me to do the math because I don't know how to. I will though after some research.
1 gallon of water weighs a little over 8 gallons. (8.34lbs)
Yes. Pressure is PSI.
You can't get equal Force along the side panels.
Since you were figuring 59.85 lbs per sq/ft. Multiplying that figure by any number will give you an answer in Sq/Ft, not linear feet.
Fuzzy Duck back again and sobber today
NolaPete your right about the pressure at a given point been the same even if the body of water is 22 miles or 22 inches in lenght.
Weight of water using the metric system is thus,
1 Mtr Square of water = 1000 ltr and this = 1000 Kg (metric system is easy that way)
so your tank messuring 144" x 98" x 60" = 3.657 x 2.489 x 1.524 Mtr = 13,871 Kg of water
Times this by 2.2046 gives you pounds = 30,580Lb of water.
Hope this can help you in your quest
NolaPete your right about the pressure at a given point been the same even if the body of water is 22 miles or 22 inches in lenght.
Weight of water using the metric system is thus,
1 Mtr Square of water = 1000 ltr and this = 1000 Kg (metric system is easy that way)
so your tank messuring 144" x 98" x 60" = 3.657 x 2.489 x 1.524 Mtr = 13,871 Kg of water
Times this by 2.2046 gives you pounds = 30,580Lb of water.
Hope this can help you in your quest
Fuzzy Duck agian,
NolaPete iv just worked out my tank (8' x 2' x 2') and the pressure using your formula originaly posted.
pressure on front = 453 kg
pressure on back = 453 Kg
Pressure on each end = 113 Kg x 2
Total = 1132 Kg of pressure on the total of the four sides
How can this be when it only holds 904 Kg of water?
Please explane
NolaPete iv just worked out my tank (8' x 2' x 2') and the pressure using your formula originaly posted.
pressure on front = 453 kg
pressure on back = 453 Kg
Pressure on each end = 113 Kg x 2
Total = 1132 Kg of pressure on the total of the four sides
How can this be when it only holds 904 Kg of water?
Please explane
Are my posts being ignored?
You can't get an equal Force on the entire surface of the glass sides.
2'H / 2.31 = .865psi
96 * 24 = 2304 sq/in
Your tank has about 1992.86 lbs of water.
This also means at a depth of 24", you have 1992.86lbs of horizontal thrust pushing on the bottom of each glass side.
You can double check that with the weight of 1 gallon of water. It will be close.
96 * 24 * 24 = 55296 cu/in
55296 / 231 = 239.37 gallons
239.37 * 8.34 = 1996.34 lbs
