# Fluid Mechanics in a Closed System

Mechanics

Oct 24, 2013 (4 years and 6 months ago)

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Fluid Mechanics in a Closed
System

Pascal’s Law

states in a closed system, an
increase of pressure at any point will
produce an equal increase in the pressure at
every point in the liquid.

Difference between force and pressure:

Pressure is exerted on a unit area.

Consider a glass flask. Fill it to the top and
insert stopper into the neck. If you hit the top
of a 1 sq in stopper with an 18 lb force, what
pressure is exerted on the 25 sq. in bottom?

Pressure is transmitted through a liquid.

If the system is closed with equal piston area,
we will have equal inputs and equal outputs.

If the system is “U” shaped, the direction of
the force can be changed.

One force down = One force up

The shape of the container has no effect on
the pressure in it. We could connect the
equal piston through a “small hose” and
move our equal force anywhere we want it.

Suppose the pistons have different areas.
Then the forces are different and the
distance moved are different.

If we connect two pistons in a closed system,
the distance moved is inversely proportional
to their areas. Volume remains constant.

A

B

C

D

Force

500 #

25 #

Area

20 sq in

30 sq in

60 sq in

Pressure

Length

6 in

Volume

A

B

C

D

E

F

Force

11200#

13440 #

Area

5 sq in

12sq in

10sq in

Pressure

1600
psi

2240 psi

Length

12 in

Volume

51.4 cu
in