Forces Due to Static Fluids

Question 1

What is the function of the air pressure in a pneumatic cylinder?

Answer 1

The air pressure acts on the piston face, producing a force that causes the linear movement of the rod. F=PA where A=pi(r)^2

Question 2

What effect does pressure have on the end of the cylinder?

Answer 2

The pressure acts on the end of the cylinder, tending to pull it apart.

Question 3

Why are there four tie rods in a pneumatic cylinder?

Answer 3

The tie rods are necessary to prevent the cylinder from being pulled apart by the pressure.

Question 4

How is the distribution of pressure within a gas described?

Answer 4

The distribution of pressure within a gas is very nearly uniform.

Question 5

Horizontal Flat Surfaces Under Liquids?

Answer 5

F = PA
Force would be the same because
the pressure at the bottom is dependent
only on the depth and specific weight
of the fluid in the container.
Recall Pascal’s paradox

Question 6

Pressure of fluid against a vertical rectangular wall characteristics?

Answer 6

a) Fresultant= Pavg.Area
Pavg= yh/2
Area= area of wall (h=L)

b) C.O.P: distance to centroid
C.O.P= h/3

c) Lc=hc= vertical distance from free surface to centroid
Lp=hp= vertical distance from free surface to midpoint of h (where pavg acts).

Question 7

Pressure of fluid against a slanted rectangular wall (dam) characteristics?

Answer 7

a) Fresultant= Pavg.Area
Pavg=yhp=yh/2
Area=L.W
Length is related to the height by the angle .

b) Everything else is the same as a vertical wall.

Question 8

Submerged surfaces characteristics?

Answer 8

a) Fresultant= Pavg.Area
Pavg=yhc/2
Area=area of wall submerged

b) hc= vertical distance from free surface to centroid of area of wall submerged
hp= From free surface to C.O.P

c) C.O.P= always below centroid
C.O.P=Lp= Lc+Ic/L.Area
Area of wall submerged
C.O.P=hp=hc+(Lcsin^2)/hc.Area

d) Ic= Moment of Inertia of wall submerged. Make use of geometric property.

Question 9

Piezometric head?

Answer 9

When no ventilation exists there air is now pressurized (Pa exists above fluid)

Question 10

Ways to solve pressure upon piezometric head?

Answer 10

a) Convert Pa into depth of the fluid. To obtain equivalent depth from Pa in relation to fluid.

ha=Pa/yfluid

b) equivalent depth=new total depth= h= ha+hfluid

c) Treat the rest of question as submerged surface case.