Forces in Fluids

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Forces in Fluids
Chapter 13
What is pressure?
The result of a force
acting over a given
area.
Pressure =
Force/Area
What label?
N/m2
1 N/m2 is known as
a pascal (Pa)
Blaise Pascal
1623-1662
French physicist and
mathematician
Performed some of
the first experiments
dealing with
pressure
Fluid pressure
Fluids: a substance that attains the
shape of its container. Examples: both
liquids and gases.
Fluid pressure changes with depth in a
column of water and with altitude.
Fluid pressure in water does not depend on
the volume or weight only the depth.
Air Pressure
Air pressure at sea
level is approx. 101
kPa.
Air pressure will
decrease with
increases in altitude.
Examples: flying in a
plane, driving in the
mountains
Pascal’s Principle
A change in
pressure at any
point in a fluid is
transmitted
equally and
unchanged in all
directions
throughout the
fluid
hydraulics
Uses Pascal’s principle and moving
pistons with an enclosed pressurized
fluid:
Examples:

Car brakes, jacks, and loaders
Problem:
If a force of 30 N is placed on a small
piston of a hydraulic device with an area
of 2 cm2, what size of a load can the
larger piston lift if the area of the larger
piston is 80 cm2?
Bernoulli’s principle
Swiss scientist
1700-1782
Explained the basis
behind airplane
flight.
As the speed of a
fluid increase, the
pressure decreases
Airplane forces:
Why is wing shaped the
way it is?
Other applications of
Bernoulli’s principle:
buoyancy
The ability of a fluid to exert an
upward force on an object resulting in
an APPARENT loss of weight of the
object
Archimedes
Greek
mathematician
287-212 B.C.
Best known for his
theory that the
buoyant force on an
object is equal to the
weight of the fluid
displaced
Application of buoyancy
Ballast tanks in submarines
“submarine” fish
Assignment:
Pages 407-408
 1-10, 12, 15, 17, 20, 26, 27
 Page
 1-6
409

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