f2 sc c6 air pressure
TRANSCRIPT
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Air Pressure
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6.1 Understanding Air Pressure
• The kinetic theory of gases
states that gas consists of tiny
particles.
• These particles are constantly
in random motion and collide
against the walls of the
container.
• These collisions produce the
gas pressure.
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Atmospheric Pressure
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Atmospheric pressure
• The thick layer of air surrounding the Earth is called
the atmosphere.
• The air particles in the atmosphere collide with one
another and collide against the surfaces of all things.
• These collisions result in air
pressure or
atmospheric pressure.
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GAS PRESSURE AND ATMOSPHERIC PRESSURE
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Atmospheric pressureAtmospheric pressure
• Atmospheric pressure decreases with the
altitude or the height above sea level.
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Show existence of atmospheric pressureShow existence of atmospheric pressure
• The cardboard does not fall and the
water remains in the glass even
though it’s not supported by
anything.
• Explanation:
The force caused by the
atmospheric pressure acts on the
surface of the cardboard is greater
than the weight of the water in the
glass.
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Show existence of atmospheric pressureShow existence of atmospheric pressure
• When a can filled with hot
water is closed and is cooled
down rapidly by pouring cold
water on it, it will crash
instantly.
• Explanation:
When the air inside the can is
cooled, its pressure decreases.
The high atmospheric pressure
outside exerts a great force on
the can and causes it crashes.
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Instrument Used to Measure Atmospheric PressureInstrument Used to Measure Atmospheric Pressure
-Fortin Barometer
-Aneroid Barometer
-Simple Barometer
Aneroid BarometerFortin Barometer Simple Barometer
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• Atmospheric pressure is 76 cm mercury at sea
level. The unit of air pressure is atmosphere
and the air pressure near sea level is one
atmosphere.
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Low pressure or high pressure Low pressure or high pressure
• If in some area the pressure is higher than it is
in the surrounding area, we say that it is an
area of high pressure.
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Air pressure
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GAS PRESSURE AND ATMOSPHERIC PRESSUREGAS PRESSURE AND ATMOSPHERIC PRESSURE
• Gas pressure is the force per unit area
exerted by the gas molecules the gas molecules as they collide
with the walls of their container.
• Atmospheric pressure is the pressure caused
by the weight of the air weight of the air above us.
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• The factors which affect the air pressure are:
(a) Volume of air
(b) Temperature of air
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Volume of the container
• When the volume of the container is reducedvolume of the container is reduced, the air
particles become closer.
• The air particles collide more frequently among
themselves and against the walls of the container.
Hence, the air pressure increasesair pressure increases or vice versa.
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Temperature
• When the temperature is increasedtemperature is increased, the air
particles gain more energy and move faster.
• The rate of collisions between the particles
and against the walls increases.
• This increases the air pressureincreases the air pressure or vice versa.
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Application of air pressure
• Drinking straw
• Rubber sucker
• Syringe
• Vacuum cleaner
• Lift pump
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Drinking Straw
• When the water is sucked,
the air inside the straw is
sucked out.
• The air pressure inside the
straw is reduced.
• The higher air pressure
outside the straw forces
the water to enter the
straw.
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Syringe
• When the piston is pulled, the air pressure in the syringe decreases.
• The higher air pressure outside forces the liquid into the syringe.
• When the piston is pushed, the air pressure in the syringe increases .
• The higher pressure in the
syringe forces the liquid to
flow out.
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Rubber sucker
• The higher air pressure
at Y presses the pump
and it sticks firmly on
the surface of wall.
• The air pressure that
presses on it is enough
to support light
objects.
Y
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• When the plunger is
pulled upwards, the
higher pressure in Z
forces the blockage
out.
ZZ
Plunger / Suction pump
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• The air pressure at P
is higher.
• It pushes the water
up the siphon to
beaker Q.
Siphon
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6.3 Gas under High Pressure
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Gas cylinder
• When gases are compressed under high
pressure, they turn into liquids.
• This property is used in the storage of gas in
gas cylinders.
• A larger volume of
gas can be stored in
the form of liquid.
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Aerosol cans
• Similarly, perfumes, insecticides and paints
can be stored in the form of liquids in aerosol
cans.
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Safety precautions when using gas
under high pressure.
(a) Gas cylinders should be kept away from heat
sources.
(b) Gas cylinders should be placed vertically.
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( c) Gas cylinders should be kept in rooms with
good ventilation.
(d) Always check the gas cylinders for leakage.
(e) Light a match first before turning on the gas.
Safety precautions when using gas
under high pressure.
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