Fluids & Pressure Objectives: 1.define fluid, liquid, gas, pressure, Pascal, barometer, aneroid 2....
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Transcript of Fluids & Pressure Objectives: 1.define fluid, liquid, gas, pressure, Pascal, barometer, aneroid 2....
Fluids & Pressure
Objectives:
1. define fluid, liquid, gas, pressure, Pascal,
barometer, aneroid
2. write two equations for pressure
3. state Boyle's Law
4. describe some examples of pressure
Basic Definitions
fluid anything that flows
liquid definite volume, indefinite shape
gas indefinite volume, indefinite shape
Pressure force per unit of area
- measured in
pascals (Pa)
pounds per square inch (psi)
torr
atmospheres (atm)
millimeters of mercury (mm Hg)
kilopascals (kPa)
millibars (mb)
- conversion factors
1 atm = 760 torr = 1013 mb = 101.3 kPa = 14.7 psi = 760 mm Hg
- increases if force increases or area decreases
Pressure Equation #1
P = F ÷ A
key:
P = pressure (in Pa)
F = force (in N)
A = area (in m2)
Pressure and Depth
in a fluid, depends on depth more fluid above increases the force
pressure is exerted in all directions
Pressure Equation #2
P = ghkey:
P = pressure (in Pa)
= density (in kg/m3)
g = 9.81 m/s2
h = depth (in m)
Boyle’s Law
for an enclosed gas, an increase in pressure will decrease the volume
if the pressure is doubled, the volume is cut in half
Boyle’s Law Equation
P1V1 = P2V2
Key:
P1 = pressure at beginning
V1 = volume at beginning
P2 = pressure at end
V2 = volume at end
Real World Applications
Air Pressure air in atmosphere has a weight
(3 square feet = roughly 220,000 pounds) measured with a barometer Two Types
wet - tube of liquid inverted in a dishincreases in outside pressure force
more liquid up the tube aneroid - partial vacuum can
increase in outside pressure causes can to collapse more
Barometers
• invented by Evangelista Torricelli in 1643• filled tube with mercury • inverted tube in dish of mercury • column of mercury fell so that it was
760 mm tall • the area above the column of mercury
is a vacuum • if he used water, the tube would have
been 10.3 m tall • maximum useful straw length is 10.3 m • water will not rise more than 10.3
meters because of air pressure
Mercury Barometer
Water Pressure
pressure increases with depth
submarines made of steel to withstand the pressure on all sides
caissons for Brooklyn Bridge needed to be filled with compressed air to prevent being
crushed by the water around them
dams are wider at the bottom to resist increased pressure
Boyle’s Law
air bubbles expand as they rise through water
divers do not hold their breath as they rise or their lungs will explode