Go Back   Physics Help Forum > High School and Pre-University Physics Help > Thermodynamics and Fluid Mechanics

Thermodynamics and Fluid Mechanics Thermodynamics and Fluid Mechanics Physics Help Forum

Reply
 
LinkBack Thread Tools Display Modes
Old Jun 24th 2018, 04:44 PM   #1
Junior Member
 
Join Date: Jun 2018
Posts: 2
Hydrostatic force on side of tank

Hi,

I would like to know how to calculate the force on side of a water storage tank.
Given the water tank size is L=5m, W=4m, H=3m. The tank is fill with water up to 3m high.

What is the hydrostatic force exerted on the wall of the storage tanks at
a) 1m high
b) 2m high
c) 3m high
d) and at the base of the tank?

Appreciate your help.
piupiu is offline   Reply With Quote
Old Jun 24th 2018, 10:00 PM   #2
Senior Member
 
Join Date: Apr 2017
Posts: 319
The force on the wall of a tank or on the bottom, comes from the height of water above the point you are considering ...

The easiest way to consider this is to remember that 10.33 m of water gives one atmosphere in pressure .... so if you take a lung full of air at the surface , and swim down to a depth of 10.33m , the air in your lungs will be compressed to half the original volume ... you experience 2 atmospheres pressure at that depth ....

In your tank the deepest water is 3m ...at that depth pressure is 3/10.33 about 0.29 atm.

At 2 meters pressure is 2/10.33 about 0.19 atm ...

so the pressure on the wall varies , falling to zero at the water surface ....

I'm sure another member can solve this problem in a more tidy manner...

Last edited by oz93666; Jun 24th 2018 at 10:03 PM.
oz93666 is offline   Reply With Quote
Old Jun 25th 2018, 02:50 AM   #3
Senior Member
 
Join Date: Oct 2017
Location: Glasgow
Posts: 194
Originally Posted by piupiu View Post
Hi,

I would like to know how to calculate the force on side of a water storage tank.
Given the water tank size is L=5m, W=4m, H=3m. The tank is fill with water up to 3m high.

What is the hydrostatic force exerted on the wall of the storage tanks at
a) 1m high
b) 2m high
c) 3m high
d) and at the base of the tank?

Appreciate your help.
The pressure difference relative to the adjacent atmospheric layer due to a liquid is

$\displaystyle \Delta P = \rho g \Delta z$

where $\displaystyle \rho$ is the density of the fluid, g is the gravitational acceleration (9.81 m/s$\displaystyle ^2$) and $\displaystyle \Delta z$ is the depth. If you assume that there's terrestrial air above the water, the pressure of the adjacent layer is 101325 Pa. Then, the pressure difference from this value can be calculated if you substitute for the density of water and the Earth's gravitational acceleration.
benit13 is offline   Reply With Quote
Old Jun 25th 2018, 06:01 AM   #4
Junior Member
 
Join Date: Jun 2018
Posts: 2
I am referring to the hydrostatic force not pressure.
piupiu is offline   Reply With Quote
Old Jun 25th 2018, 07:09 AM   #5
Senior Member
 
Join Date: Oct 2017
Location: Glasgow
Posts: 194
Originally Posted by piupiu View Post
I am referring to the hydrostatic force not pressure.
Okay, but force is just pressure multiplied by area, so once you have the pressure the force is easily obtained by multiplying it by the surface area of the tank at the height required.
benit13 is offline   Reply With Quote
Old Jun 25th 2018, 07:13 PM   #6
Senior Member
 
Join Date: Apr 2017
Posts: 319
Originally Posted by piupiu View Post
Hi,

I would like to know how to calculate the force on side of a water storage tank..
OK ..fair enough .. lets take the side 3m by 5m ....=15 square meters

So you want to find the force that is pushing on that whole wall

We saw in my previous post the pressure under 3 m of water depth is 0.2904 Atmospheric pressure , or 29.4 KPa (KN/m squared)...

But at the top of the tank the pressure is zero , and as you move down the pressure increase linearly to the max 29.4 at 3 m

So the average pressure on the wall is 29.4/2 = 14.7 KN/m squared

And the area of the wall is 15 msq ...

So force is ...15 x 14.7 = 220.5 KN or 22.05 tonnes weight

The force pushing this wall out is equivalent to the weight of 22 tonnes in earth gravity ...I kid you not ...that is correct!

And the force pushing downwards on the bottom of the tank is 60 tonnes

If the tank is resting on a flat solid surface this is no problem , the surface pushes back supporting the bottom ....

But if the tank was supported by it's edges as it might be if on a tower , the the bottom of the tank had better be strong enough to hold the weight of 60 cars without buckling! and this is a relatively small 4 by 5 meter bottom.
oz93666 is offline   Reply With Quote
Reply

  Physics Help Forum > High School and Pre-University Physics Help > Thermodynamics and Fluid Mechanics

Tags
force, hydrostatic, side, tank



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Tank and hydrostatic pressure ploplait General Physics 3 May 21st 2017 05:38 AM
pressure difference at concave side of bubble ling233 Advanced Mechanics 6 Feb 21st 2016 09:42 AM
Fluid Mechanics Problem: Hydrostatic Pressure Theprof Thermodynamics and Fluid Mechanics 1 Nov 12th 2014 03:04 PM
Which side is the north pole of a magnet? oem7110 Electricity and Magnetism 1 Jul 25th 2014 08:42 AM
Hydrostatic Force over submerged plane (should be easy) Tabur Thermodynamics and Fluid Mechanics 1 Apr 27th 2010 04:45 PM


Facebook Twitter Google+ RSS Feed