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# Hydrostatic Forces acting on a Submerged Surface

## A thrust force will act on a submerged surface

The thrust force acting on a surface submerged in a liquid can be calculated as

F = pa

=ρ g ha A                           (1)

where

F = thrust force (N)

pa = ρ g ha = average pressure on the surface (Pa)

A = area of submerged surface (m2)

ha = average depth (m)

ρ = density (kg/m3)  (water 1000 kg/m3)

g = acceleration of gravity (9.81 m/s2

### Example - The thrust force acting on the side of a container

The trust force acting on the submerged vertical side of a container can be calculated as

F = pa

= ((pt + pb) / 2) A

= (ρ g (ht + hb) / 2) A                         (2)

where

pt = pressure at the top of the submerged surface (Pa)

pb = pressure at the bottom of the submerged surface (Pa)

ht = depth at the top of the submerged surface (m)

hb = depth at the bottom of the submerged surface (m)

The thrust on a surface with width 1 m and height from 0 m to 2 m - in a water-filled container can be calculated as

F =  (ρ g (ht + hb) / 2) A

= (1000 kg/m3) (9.81 m/s2) ((0 m) + (2 m)) / 2) ((1 m) (2 m))

= 19620 N

= 19.6 kN

### Example - The thrust force acting on the bottom of a container

The trust force acting on the horizontal bottom of a submerged container can be calculated as

F =  pb A

= ρ g hb A                                     (2b)

The thrust on a bottom with width 1 m and length 2 m - on depth 1 m - in a water filled container can be calculated as

F =  ρ g hb A

= (1000 kg/m3) (9.81 m/s2) (1 m) ((1 m) (2 m))

= 19620 N

= 19.6 kN

## Related Topics

• Fluid Mechanics - The study of fluids - liquids and gases. Involves velocity, pressure, density and temperature as functions of space and time

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## Unit Converters

Temperature

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Length

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Area

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Pressure

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9 20

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