gas pressure p
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Air Pressure
Keith Warne
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Air Pressure• Gas molecules move
rapidly in all directions.
• Collisions exert a force
on objects and the
container.
• The number of
collisions determines
the total force being
exerted.
• Increasing number of
collisions would
INCREASE Pressure.The pressure is given by
the AVERAGE FORCE
PER UNIT AREA.
Standard Atmospheric Pressure
• The pressure that supports 760.0 mm of
mercury is known as STANDARD
ATMOSPHERIC PRESSURE or 1
ATMOSPHERE. (1 atm) taken at sea level.
• Since liquid pressure can be found by
P = gh
= density of liquid = 13 590 kg/m3 (mercury)
g = gravitational field strength = 9.807 N/kg
h = height = 0.7600 m
p = gh = (13590)(0.76)(9.807) = 101 300 Pa Pa =
1atm
H = 760mm
1 Pa = 1 N/m2
ATMOSPHERIC
pressure
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Water Barometer• The pressure that supports 760.0 mm of
mercury is known as STANDARD
ATMOSPHERIC PRESSURE or 1
ATMOSPHERE. (........................) taken at
sea level.
• What would the equivalent height of
water be?
• Since liquid pressure can be found by
P = gh
= density of water = .................kg/m3
g = gravitational field strength = 9.807 N/kg
h = height = ...........?? m
p = gh
ATMOSPHERIC
pressure
WATER!WATER!
H = ?? m
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Atmospheres mm Hg kPa
1 760 100
2 ??? ???
0.5 ??? ???X ??? X ???
X ??? X ???
atm
kPa
Pressure Conversions
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Aneroid Barometer
• An aneroid barometer has
a vacuum chamber that
expands or contracts
with changes in air
pressure.
• The
expansion/contraction
causes a series of levers
to pull on a chain that is
connected to a spindle.
• The spindle turns and
moves the needle
attached to it on the dial,
showing the air pressure. From World Book © 2002 World Book, Inc., 233 N.
Michigan Avenue, Suite 2000, Chicago, IL 60601. All
rights reserved. World Book i llustration by Zorica Dabich
HIGHPRESSURE
HIGH PRESSURE
HIGH PRESSURE
Aneroid Barometer
CHANGE
LOW PRESSURE
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Pressure Demonstrations - Plunger
High Pressure
If the plunger
is forced
down the air is
forced out of
the cavity.
Low Pressure
If the plunger is pulled up –
the pressure inside the cavity
is DECREASED so the
atmospheric pressure on the
outside is GREATER and it
holds the plunger against the
surface.
Air escapes!
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Heated air escapes replaced
by STEAM
Can crushing Experiment
Water boils - atmospheric
pressure balanced by steam
inside.
Steam condenses to water – no gas
inside to balance atmospheric pressure
– ATMOSPHERE CRUSHES CAN!
WATER
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Ball Pressure• A ball needs pressurized
air inside it to enable it to bounce.
• The higher the pressure the better (HIGHER) the ball will bounce.
• If the atmospheric pressure increases a higher pressure will be needed in the ball.
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Aerodynamics & Air Pressure
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Pumping air out of the jar causes the balloon to inflate!
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Hi -
This is a SAMPLE presentation only.
My FULL presentations, which contain loads more slides (with all the gaps filled in) as well as
other resources, are freely available on my resource sharing website:
www.warnescience.net
(paste into your browser if link above does not work)
Have a look and enjoy!
Keith Warne
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