pressure in fluid systems
DESCRIPTION
UNIT 3. Pressure in Fluid Systems. Unit 3 Pressure Pages 43-60. Fluid Hydraulic System Pneumatic System Density Specific gravity Buoyant force. Hydrometer Pressure PSI Atmospheric Pressure Absolute pressure Gage pressure Manometer. Pressure in a Fluid System. Unit 3 Review - PowerPoint PPT PresentationTRANSCRIPT
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Pressure in
Fluid Systems
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Unit 3 Pressure Pages 43-60 Fluid Hydraulic
System Pneumatic
System Density Specific gravity Buoyant force
Hydrometer Pressure PSI Atmospheric
Pressure Absolute pressure Gage pressure Manometer
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Pressure in a Fluid System
Unit 3 Review
Page 53 #1-15
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Fluid
Gas or liquid that conforms to the shape of the container
“Anything that flows”
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Hydraulic system
Uses liquid as the fluid
Pneumatic system
Uses air or gas as the fluid
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Why does a hot air balloon float?Why does motor oil rise to the top of water?
Density Amount of matter in a given
amount of substance
= Mass/Volume
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Density
SI measured in: Kg/m3 or gm/cm3
English measured in: Lbm/ft3 or lb/ft3
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Density
What is the density of gold if you have a 1.036cm3 piece that had a mass of 20grams?
D=m/v D=20g/1.036cm3
D=19.3g/cm3
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Density
What is the density of gold if you have a 3.108cm3 piece that had a mass of 60grams?
D=m/v D=60g/3.108cm3
D=19.3g/cm3
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Other Densities Platinum Diamond Chromium Tin (white) Tin (gray)
21.45 3.5-3.53 7.15 7.265 5.769
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Density
What is the mass in grams of mercury with a volume of 1cm3?
D = m / v 13.6 g/cm3 = x / 1cm3
13.6 g = x
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Density
What is the mass in kilograms of balsa wood with a volume of 1m3?
.3g / cm3 = x / 1,000,000cm3
300,000 g = x 300 kg =x
1m3 = __cm3
1m3 = 100cm x 100cm x 100cm
= 1,000,000 cm3
D = m / v .3g / cm3 = x / 1m3
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Specific Gravity Density of a substance divided
by the density of water
Because specific gravity is density/density the units
cancel out and is written as a whole number
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Specific Gravity Copper has a density of
8.9g/cm3
What is its specific gravity?
Specific Gravity = density of substance = density of water S.G. = (8.9g/cm3) / (1.0g/cm3) S.G. = 8.9
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Buoyant Force
The upward force on a
substance from a fluid
Will lead sink or float in water? Will it sink or float in mercury?
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Hydrometer
Instrument that measures density or
specific gravity of fluids
Can you drown in quick sand?
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Pressure Force per unit area exerted by a fluid
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Force on Airplane Windows
An airplane window has a surface area of 136 square inches.
Air pressure inside the cabin is 12.3 lb/in2
The force pushing on the window
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Pressure What happens to the
pressure as we move away from the earth?
http://www.sciencedaily.com/videos/2006/1201-home_runs_amp_holeinone.htm
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Force on Airplane Windows
An airplane window has a surface area of 144 square inches.
Air pressure inside the cabin is 14.7 lb/in2
Air pressure outside the window is 6.7 lb/in2
The force pushing on the window The force pushing out on the window
Net force on window
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Inward force on window
F = P x A F = (14.7lb/in2)(144in2)
F = 2116.8 lb
F = P x A F = (6.7 lb/in2)(144in2)
F= 964.8lb
Outward force on window
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Net Force on window
The window is being pushed outward with a net force of
1152 lb.
Net Force = Force out – Force in Net Force = 2116.8 lb – 964.8 lb
Net Force = 1152 lb
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Net Force on window If the plane rises to a higher altitude and the pressure outside
the plane changes to 5.4 lb/in2
How much stronger will the windows need to be in order to
hold the pressure
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Inward force on window
F = P x A F = (14.7lb/in2)(144in2)
F = 2116.8 lb
F = P x A F = (5.4 lb/in2)(144in2)
F= 777.6lb
Outward force on window
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Net Force on window
The window was originally pushing outward with a net force of 1152 lb.
Therefore it needs to hold 187.2 more pounds of pressure (1339.2 – 1152)
Net Force = Force out – Force in Net Force = 2116.8 lb – 777.6 lb
Net Force = 1339.2 lb
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Pressure Pressure acts equally in all
direction at any point in a fluid and therefore it is a scalar
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Absolute vs. Gage Pressure
When we fill a tire to 30lb/in2 is that the absolute or the gage pressure?
Atmospheric pressure = 14.7 lb/in2
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Absolute Pressure
Total pressure compared to a perfect vacuum
Gage Pressure Pressure measured above
atmospheric pressure
G.P = Total pressure – atmospheric pressure
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Total Pressure
Gage pressure is generally
measured “with a gage”
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Pressure
Tire gage reads 30lb/in2
What is the atmospheric pressure? What is the gage pressure? What is the total pressure?
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Pressure Tire gage reads 30lb/in2
What is the atmospheric pressure?
What is the gage pressure?
What is the total pressure?
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How does pressure change with depth?
Where is the pressure greater the shallow end or the deep end?
Why?
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Pressure increases with depth
There is more water sitting on top of the deep end
There is twice as much weight Twice as much force
Twice as much pressure
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Relationship between pressure and depth
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Water Pressure Calculation
Given: The height of the water in a storage tank is 100 ft above the
valve. The weight density of water is 62.4 lb/ft3
Find: The pressure at the valve in lb/ft2
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Water Pressure Calculation
P = pw x h P = (62.4 lb/ft3)(100ft)
P = 6240 lb/ft2
Given: 1 ft2 = 144 in2
Now find: Pressure in PSI
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Water Pressure Calculation
P = pw x h P = (62.4 lb/ft3)(100ft)
P = 6240 lb/ft2
Given: 1 ft2 = 144 in2
p = (6240 lb/ft2)(1ft2/144in2)
P = 43.3 lb/in2 (psi)
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Hydraulic lift Liquids are incompressible
Air compressor increases the
pressure to the fluid
Large pushing force is exerted
on the lifting piston
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Pressure acts like forces
Pressure is a prime mover
Measuring Pressures
Manometer – instrument used to measure fluid pressure
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Balanced pressure across the valve
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Unbalanced pressure across the valve
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Pressure on bottom does not depend on the size of the tank
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Hydraulic jack?
Large cylinder to a small cylinder Same pressure = more force in the smaller
cylinder Small to large = allowable force but small
increments?