Existence of Gas pressure based on the kinetic theory gas molecules move freely and randomly. The...
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3.3 Understanding gas pressure and atmospheric pressure
Existence of Gas pressure based on the kinetic theory gas molecules move freely and randomly. The gas molecules collide with one another and also collide
Existence of Gas pressure based on the kinetic theory gas
molecules move freely and randomly. The gas molecules collide with
one another and also collide with the walls of their container. The
collision of gas molecules with one another is an elastic
collision
Slide 3
The collision of gas molecules with the wall of the container
produces change of momentum or impulsive force So the gas molecules
exert a pressure on the inside of the container because pressure is
force per unit area ( P = F ) A ..
Slide 4
The conclusion about gas pressure Gas pressure is the force per
unit area exerted by the gas molecules as they collide with the
walls of their container.
Slide 5
What happen if the volume inside a container decreases? The
rate of collisions between the gas molecules with the walls of the
container increase Therefore the pressure of the gas increases
..Volume decreases, pressure increases.. ( what law ??????)
Slide 6
What happen if the container is heated? The velocity of the gas
molecules increase The kinetic energy of the gas molecules
increase
Slide 7
The collision rate between the gas molecules with the walls of
container increase So the force of collisions will increase
Therefore the pressure of the gas increases ..Temperature
increases, pressure increases ( what law???????)
Slide 8
Measuring Gas Pressure 1.Manometer
Slide 9
P gas = P atmosfera + h manometer
Slide 10
Pgas = Patmosfera - h
Slide 11
P gas = P atmosfera
Slide 12
Example 1 Calculate the pressure of the gas supply in the units
(i) cm Hg (ii) Pa [ Density of mercury = 1.36 x 10 4 kg m -3 and
Atmospheric pressure = 76 cm Hg ]
Slide 13
2. Bourdon Gauge
Slide 14
Bourdon gauge
Slide 15
The another use of U-Tube The U-tube can also be used to
determine the density of a liquid. Pressure P 1 = Pressure P 2 h 1
1 g = h 2 2 g h 1 1 = h 2 2
Slide 16
Example 2 The figure shows a U-tube use to determine the
density of a liquid K. When liquid K is poured into one arm, the
water level in the other arm rises. If the density of water is 1
000 kg m -3, determine the density of liquid K.
Slide 17
Existance of Atmosheric The gas molecules in the air possess
mass and experience the pull of gravity. The result is that gases
have weight. The weight of the gas molecules will produce force and
as a result will exert pressure on you because pressure is force
per area ( P = F ) A The pressure is called the atmospheric
pressure.
Slide 18
Characteristics of Atmospheric Pressure acts equally in all
directions pressure on any object is not dependent on the surface
area of the object. influenced by the altitude. (Hence as the
altitude increases, the atmospheric pressure decreases because the
higher it is from the surface of the Earth, the lower is the
density of air.) -The value of atmospheric pressure at sea level is
approximately 1 atm = 1x 105 Pa = 76 cm Hg = 10 m of water.
Slide 19
Example 3 The atmospheric pressure is 76 cm Hg. Calculate the
atmospheric pressure in the units Pa. [Density of mercury = 1.36
x10 4 kg m -3 ].
Slide 20
Measuring atmospheric pressure The Simple Fortin barometer
Slide 21
The mercury column rises or falls according to the pressure of
air on the mercury in the dish. The space above the mercury column
is a vacuum so it exerts no pressure on the top of the mercury
column. If the vertical height of the mercury is h cm, therefore
the atmospheric pressure reading is h cm mercury .
Slide 22
BAROMETER
Slide 23
What happen to a column Of mercury if a barometer is taken to
the bottom of the sea and why? What happen to a column of mercury
if a barometer is taken to the top of a mountain and why? THINK
!!!!!
Slide 24
Example 4 The figure shows a mercury barometer is placed in a
school laboratory where the atmospheric pressure is 75 cm Hg.
Slide 25
If the density of mercury is 1.36 x 104 kgm-3 and the density
of water is 1 x 103 kgm-3, determine (i) the atmospheric pressure
in the units Pa (ii) the value of h if the mercury is replaced by
water. (iii) the value of h if the barometer is submerged in water
at depth of 40.8 cm.
Slide 26
Aneroid Barometer
Slide 27
When the atmospheric pressure decreases, the container will
expand. When the atmospheric pressure increases, the container will
constrict. The slight movement of the box is magnified by a lever
system which is connected to a pointer. The Aneroid barometer can
be used as an altimeter by mountaineers or in an aeroplane to
determine its altitude.
Slide 28
BAROMETER ANEROID
Slide 29
Slide 30
Applications of Atmospheric Pressure (i) Drinking straw