1. Elementary Mechanics of Fluids
CE 319 F
Daene McKinney
Elementary Mechanics of Fluids
Hydrostatic Forces on Plane Surfaces

2. Pressure on Plane Surface
Surfaces exposed to fluids experience a force due to the pressure distribution in the fluid
Centroid
Center of pressure F

3. Example
2.44 m
Concrete
(23.6 kN/m3)
Plywood Form
(2.44m x 1.22m) F

4. Line of Action of Force
Lies below centroid, since pressure increases with depth
Centroid
Center of pressure F

5. Example (3.59) F  as H ?  as H ? is constant as H ? T  as H ?
T is constant as H ? F T

7. Find: Force of block on gate
Example (3.73)
Find: Force of block on gate F
Fw,g
Fb,g
0.133 2

8. Example (3.78) F RA 6

9. HW (3.87)

10. HW (3.92)

11. Example Given: Gate AB is 4 ft wide, hinged at A.
Gage G reads psi
Find: Horizontal force at B to hold gate.
Solution:
6 ft A B G
Oil
SG=0.75
Water
Air
5.01 ft
18 ft
gate
Convert negative pressure in
tank to ft of water

12. Example Fw Foil FB A 3.03 ft 4ft B 6 ft A B G Oil SG=0.75 Water Air
gate

13. HW (3.96)

14. HW (3.102)