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Join Date: Oct 2017
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# Force Calculation

10/02/2017 1:04 AM

How do I calculate the force required to lift a piston that pushes upwards into an open tank ( like a spring stopper in a bath ) where the tank dimensions are 50cm by 50cm and 3 m tall? The tank being filled with water.

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#1

### Re: Force calculation

10/02/2017 1:52 AM

Approx 4 psi x area of stopper hole in square inches.

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#2

### Re: Force calculation

10/02/2017 2:01 AM

The force (F) required to move an object of mass (m) with an acceleration (a) is given by the formula F = m x a. ...Take a spring scale and use it to measure the required weight to move the stopper...

http://www.wikihow.com/Calculate-Force

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#3

### Re: Force calculation

10/02/2017 3:45 AM

Using the basic Physics taught in the second year of secondary school, and either a pocket calculator, a slide rule, or a book of logarithm tables.

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#4

### Re: Force calculation

10/02/2017 3:56 AM

Pressure = h*ρ*g. Force = pressure*plug area. Only the height comes into it. The 50 x 50cm is irrelevant.

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#8

### Re: Force calculation

10/02/2017 3:04 PM

Teachers like to include irrelevant data to throw off people who don't understand the underlying concepts. Very effective in determining who understands the principles even if they made a mistake in their calculations.

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#5

### Re: Force Calculation

10/02/2017 10:42 AM

A stopper in a bath tub and a piston in a cylinder have two different objectives. The stopper is to seal only. The piston is to seal and move.

So you need to calculate the sum of the forces the weight of the piston, the weight of the water column and the frictional force of the seal.

Good luck with that.

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#6

### Re: Force Calculation

10/02/2017 11:42 AM
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#7

### Re: Force Calculation

10/02/2017 12:49 PM

You provided insufficient information for the correct answer to be divulged here.

Radius of stopper = X, m, mass of piston = Y, friction of piston against seal =Z

Area of stopper = ΠX2 m2

Guess: X = 0.0129 m (One inch diameter stopper)

A= 0.000522792 m2

Mass of water in 3 m column of that area:

M= V•ρ, where ρ=1000 Kg/m3 (at the triple point of water)

V= 0.0015683773 • 1000, M=1.5683773 Kg

it requires a 1.5683773 Kg force (in standard gravity),

15.380527 Kg-m/sec2 or 15.380 Newtons, if mass of piston and frictionof seal are ignored.

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#13

### Re: Force Calculation

10/04/2017 5:48 PM

I do wonder about the bouyancy of the plug/cylinder....and whether the line directly below the plug/cylinder is filled with water with no air voids, vented with air, or otherwise....and at what pressure/temperature.

It also says the tank is being filled with water. How exactly that is occuring coukd be very important.

....and what about the righting moment of the plug/cylinder?

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#14

### Re: Force Calculation

10/05/2017 10:44 AM

Good points, especially about plug buoyancy, and righting moment.

The information provided was at a sophomore or freshman level of sketchiness.

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#9

### Re: Force Calculation

10/03/2017 9:49 PM

Consider a cylinder the size of your piston and the height of the water. How much does that much water weigh? That is the amount of force needed to lift the piston.

If you want to get exact, as the piston rises, the water level rises, though not as much as the piston. The force will be the weight of water the size of the piston and the height between the piston and the top of the water. This height decreases slightly as the piston rises, so the force decreases slightly as the piston rises.

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#10

### Re: Force Calculation

10/04/2017 3:40 AM

"...The tank being filled with water...."

From where? Up from below the piston? That wilp make things much more complicated. The shape of the piston and the cylinder opening would need to be known, as well as flowrate, and more.

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#11

### Re: Force Calculation

10/04/2017 2:00 PM

Dear Poster

Many tried to answer you. But-

Right force calculation can be derived only, If you can insure that you put all the possible force in phrasing of question.

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#12

### Re: Force Calculation

10/04/2017 2:21 PM

A truer statement cannot be spoken.

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#15

### Re: Force Calculation

10/10/2017 9:39 AM

Vessel thickness = 3/16" => 234 Kg

If vessel 100% full of water => 750 Kg

Minimum total weight => 1000 Kg

GO TO STORE TO PURCHASE A PISTON TO LIFT 2 TONS (min).

(you are not going to manufacture the piston). A designer conceives everything so clear.

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