38936975 3 3 gas and atmospheric pressure

7/27/2019 38936975 3 3 Gas and Atmospheric Pressure

1/18

3.3 UNDERSTANDINGGAS PRESSURE AND

ATMOSPHERIC PRESSURE

Learning Outcome

Explain gas pressure

Explain atmospheric pressureDescribe the applications of atmospheric pressure

Solve problems involving atmospheric and gas pressure


2/18

Hands-on activity 3.3 pg 56

Aim : To gain an idea of gas pressure

Discussion

1. When air is pumped into a balloon, what

do you feel when you squeeze it ?

2. Why is there an opposing force acting on

your fingers ?

Refer text book pg 86 for the answer.

Idea of gas Pressure


3/18

Gas Pressure

Billions of air molecules insidethe balloon moves in random motion.

Air molecules collide with the innerwall of the balloon.

Force is exerted on the surface

results in air pressure in the balloon.Air pressure is the force

exerted on a surface by air

molecules per unit area of the

surface

PrForce

essureArea


4/18

Hands-on activity 3.4 pg 57

Aim : To study the existence of atmospheric

and gas pressure

Activity 1. Hot water in a plastic bottle.

Activity 2. Cardboard on the mouth of an

inverted glass.

Activity 3. Pulling two intact sink pump.Activity 4. Removing water using straw.

Can you explain each of the observation ?

Idea of atmospheric Pressure


5/18

Atmospheric Pressure

.

.

.

.

..

..

.

.

....

.

.

.

.

.

. ..... . ...

..

..

.

.

. .

.

.

.

.

...

.

.

. .

.

.

. .

.

..

.... .

.. ... ..

.

.. .. .

. .

.

.

.

..

. . . . ...

.. .

... ... .

.

.. . ...

. ..

..

..

.. . ...

.. .

...

.. .. ....

..

..

.. .

.

. .. ..

.. .. .

.. . .. .

.

.

. . .

.... .

...

..

..

.. ...

......

.......

... .... .

..

...

..

..

. ..

. .. .


6/18

Atmospheric Pressure

Atmospheric pressure is the

force exerted on the Earths

surface by air molecules of the

atmosphere per unit area of thesurface

PrForce

essureArea

Atmospheric pressure decreases with altitude.

Reason :

1.At a higher altitude, the density of the air is lower.

2. At a higher altitude, the temperature of the air is

lower, hence less collisions.


7/18

Barometer

a. Aneroid barometer

INSTRUMENTS FOR MEASURING


b. Fortin barometer

It can be used as

an altimeter


8/18

INSTRUMENTS FOR MEASURING

GAS PRESSURE

Bourdon Gauge Manometer

Gas pressure

= atmospheric pressure

+ pressure due to h cm

of mercury

mercury


9/18

VARIOUS UNITS OF


760 mm Hg

StandardAtmospheric

pressure (1 atmosphere)

0.76x 13600 x 10 Pa

= 103360 Pa

= 103360 N m-2

= 1.0336 x 105 Pa

= 1.0336 bar of pressure

10.336 m water

Mercury barometer

At sea level,

h = 760 mm

760 mm Hg

1 atm.

105 Pa

105 N m-2

10 m

water

76 cm Hg

1 bar pf

pressure


10/18

Worked Example pg 90

The reading of a mercury barometer at a

meteorological station is 745 mm mercury.

What is the value of the atmospheric pressure

at the meteorological station in pascal ?(Density of mercury = 13 600 kg m-3)

solution

Atmospheric pressure = 745 mm Hg

= 0.745 x 13 600 x 10

= 101 320 Pa

hg


11/18

Worked Example pg 90

The atmospheric pressure is 760 mmHg and the difference in themercury level of a manometermeasuring the pressure of a gas is20 mm. What is the pressure of thegas in mm Hg ?

solution

Gas pressure= Atmospheric pressure + 20 mm Hg

= 760 mm Hg + 20 mm Hg

= 780 mm Hg


12/18

Calculate the total pressure

acting on the body of a diver at

a depth of 450 m underwater.

Worked Example Exploring pg 173

(Take density of sea water = 1200 kg m-3, g = 10 N kg-1and atmospheric Pressure = 105N m-2)

solutionTotal pressure

= Atmospheric pressure + 450 m water= 105 N m-2 + 450 (1200)(10) Nm-2

= 105 + 5400000

= 5500000 N m-2


13/18

APPLICATIONS OF


Drinking Straw Rubber Sucker

Syringe Siphon


14/18

APPLICATIONS OF


Vacuum Cleaner Lift Pump

Pouring milk

from can

Lifting big piece of

glass (pg 90)


15/18

EVALUATION

1. If 10 cm3 of

mercury is added

into the bowl, what

happen to the

value of h ?

A > 76 mmB < 76 mm

C 76 mm

h = 76 mm


16/18

A P

B P and Q

C Q and R

D P, Q and R

EVALUATION

2. A barometer is placed in an

region where the atmospheric

pressure is 76 mm Hg. Which

of the diagrams shows thecorrect level of the mercury.

h = 76 mm

h = 76 mm

vapour

h > 76 mm

P Q R


17/18

EVALUATION

3. Figure shows a soft toy hung on a suction cup.

The soft toy does not fall to

the floor because thepressure in

A P > Q

B P = Q

C P < Q

D Q = 0


18/18

Home work

Mastery practice 3.3

text book pg 91

Check your progress 3.3

Exploring pg 179

38936975 3 3 gas and atmospheric pressure

Documents