Transcript Foundations of Technology Fluid Technology

Foundations of Technology
Fluid Technology
Teacher Resource – Unit 2 Lesson 6
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STEMCenter for Teaching and Learning™
Foundations of Technology
The BIG Idea
Big Idea:
Fluid technology combines
mechanics with the omnidirectional nature of fluids.
© 2013 International Technology and Engineering Educators Association
STEMCenter for Teaching and Learning™
Foundations of Technology
Fluids
Fluids have a loose molecular structure so
that they flow and take the shape of their
confining container
They may be gases
Controlling gases under pressure is called
pneumatics
They may be liquids
Controlling liquids under pressure is called
hydraulics
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STEMCenter for Teaching and Learning™
Foundations of Technology
Pressure
A fluid exerts a force
equally to all inside
surfaces of the container
holding it
Pressure is measured as
a force distributed over a
force
specific area
For example: pounds per
square inch
area
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STEMCenter for Teaching and Learning™
Foundations of Technology
Pressure: Force/Area
Pressure is caused by
the cumulative force of
random molecules of the
fluid striking the inside
surface of the container.
To see how volume and
temperature affect the
pressure of a contained
gas visit this link: PHET
Gas Properties Simulator.
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STEMCenter for Teaching and Learning™
Foundations of Technology
Hydraulics
Liquids do
not
compress
That makes
hydraulics
very useful in
efficiently
transmitting
forces
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STEMCenter for Teaching and Learning™
Foundations of Technology
Pascal’s Law
Pascal experimented with fluids during
the renaissance
Pascal’s Law states that the pressure at
any point in a body of fluid is the same in
every direction, exerting equal force on
equal areas.
So: the pressure is the same, and any change in the
pressure at one point in a confined fluid will create an
equal change everywhere in the confining vessel.
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STEMCenter for Teaching and Learning™
Foundations of Technology
Hydraulic Cylinders
These 2 fluid filled cylinders connected
by a hose represent 1 fluid container.
The piston inside each cylinder can
slide forcing some fluid from one to
the other, pushing the piston and solid
rod outward. Because it is one
container, Pascal’s Law will apply.
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STEMCenter for Teaching and Learning™
Foundations of Technology
Hydraulic Cylinders
5 lb
weight
If we apply 5 pounds of force
downward on the top piston rod 5
pounds of force should push out on
the lower piston rod. This is because
the increased pressure created by the
force in the top cylinder will be
transmitted equally to the bottom
cylinder.
5 lbs. of
force
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STEMCenter for Teaching and Learning™
Foundations of Technology
Hydraulic Cylinders
This transmission
of force will work
with a flexible or
rigid hose of
almost any
reasonable length.
Extremely small or
long connecting
hoses will create
efficiency robbing
molecular friction.
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STEMCenter for Teaching and Learning™
Foundations of Technology
Fluid Mechanical Advantage
If we vary the size of the piston from
one side of the hydraulic system to
the other we can easily create
tremendous mechanical advantage
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STEMCenter for Teaching and Learning™
Foundations of Technology
Fluid Mechanical Advantage
That’s because
force is only one
factor of
pressure – area
is the other
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STEMCenter for Teaching and Learning™
Foundations of Technology
Remember that
pressure is force
divided by area, and
Pascal’s Law states
that the pressure is
the same in both
cylinders
Fluid Mechanical Advantage
But the area that
the pressure
pushes against
is different in
these cylinders
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STEMCenter for Teaching and Learning™
Foundations of Technology
Example: if the larger
cylinder’s piston
surface is 5 times that
of the smaller cylinder
the resulting force will
be 5 times greater
The Math
2 lbs.
force in
Input
cylinder
piston
area 1
square
inch
Pascal said the pressure in the input cylinder = the pressure in the output cylinder
And we know pressure is force / area, then
Force in / area in = force out / area out
Assume that the input piston area is 1 in2 and the output piston area is 5 in2
And assume we apply 2 lbs. of force to the input cylinder’s piston rod
2 lbs./1in2 = force out/5 in2
force out = (2 lbs./1in2) x 5 in2
force out = 10 lbs.
Output
cylinder
piston
area 5
square
inches
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STEMCenter for Teaching and Learning™
Foundations of Technology
10 lbs.
force out
Hydraulics
For a more
complete
explanation of
hydraulics, please
visit this link:
http://leo.koppel.ca
/backhoe/intro.html
© 2013 International Technology and Engineering Educators Association
STEMCenter for Teaching and Learning™
Foundations of Technology
Using Fluid Technology
These fluid technology principles are
applied to many engineering solutions
from backhoes to elevators and liftgates.
© 2013 International Technology and Engineering Educators Association
STEMCenter for Teaching and Learning™
Foundations of Technology