3.3 Atmospheric and Gas Pressure 2012

[SM SAINS MUZAFFAR SYAH]]

ACTIVITY 1:Idea of Gas Pressure

1. Use a bicycle pump to pump air into a deflated ball

(a) When air is pumped into a ball, what changes do you observe in the ball?

__________________________________________

(b) How would you know when there is enough air in

the ball?

__________________________________________ __________________________________________

When you squeeze a ball filled with air, you will feel an __________ force acting from the inside of the ball. The force comes from billions and billions of air molecules striking the inner wall of the ball. The molecules are in constant ________ motion. When the molecules _________ with the inner wall of the ball, the force of collisions _________ the wall outwards. The __________ exerted on the inner wall of the ball results in the air / gas pressure in the ball.

3.3

Explain gas pressure

The gas pressure in a container is caused by the __________ of gas molecules with the walls of the container. Gas/Air pressure is the force exerted on a surface by air molecules per unit area of the surface.


ACTIVITY 2: Experiments to show the existence of the atmospheric pressure

1. Fill an empty plastic bottle with hot water until it is about a quarter full. Tighten the cap immediately and wait for a few seconds.

Observation: _____________________________________________________

The _________ from the boiling water drives out the air from the plastic bottle. The cap prevents outside _______ from flowing into the bottle. When cold water is poured on it, the steam inside the bottle __________ to water and it forms partial __________ inside the bottle. The atmospheric pressure outside which is _____________ then compress the bottle.

Explain atmospheric pressure

Atmospheric pressure is the pressure caused by the _______ of the air above us.

Atmospheric pressure acts ___________ in all directions.

Atmospheric pressure varies with the _________ of the object above sea level. It _____________ with the altitude or the height above sea level. At higher altitudes, the __________ and the temperature of the air are lower. As a result, the frequency of __________ of the molecules is lower. Hence, atmospheric pressure is __________.


2. Fill a glass with water until it is almost full. Place a cardboard over the glass. By supporting the cardboard on the top of the glass, slowly invert the glass. Slowly remove the hand that is supporting the cardboard.

The cardboard ______________ and the water ___________________ The explanation for this phenomenon is that the resultant force caused by the ____________ pressure acts on the surface of the cardboard is ________ than the weight of the water in the glass.

1. Drinking Straw When drinking from a straw, one tends to

suck the straw. This causes the pressure inside the straw _________.

The outside atmospheric pressure is _________ will then act on the surface of the water in the glass, causing it to rise up the straw.

2. A rubber sucker which is ________ onto a flat smooth surface cannot be easily removed from the surface.

When the cup of the rubber sucker is leveled, the ______ from the lower portion of the cup will be crushed out

A _____ pressure area will be formed in the cup. A higher ___________ pressure will now press the sucker firmly onto the surface.

3. Syringe

When the piston of the syringe is pulled upwards, a ______ pressure zone is created within it.

The _________ atmospheric pressure will push the water into the syringe.

Describe the applications of atmospheric pressure


5. Vacuum Cleaner A fan sucks out the ________ from space A . The pressure inside the vacuum cleaner is ________. The atmospheric pressure is ___________ than the pressure inside the vacuum cleaner. The dust and dirt is __________ into the cleaner. The bag acts as a filter, stopping the dust and dirt, but not the air.

4. Siphon A siphon is very useful for removing liquids from a tank or a fixed container. For example, dirty water is sucked out of an aquarium. It consists of a tube which has been filled with liquid and one end of it is placed in a tank.

The water pressure is the______________ as the atmospheric pressure at A, B and C.

The water pressure at D = atmospheric pressure + h ρ g

The _________________water pressure causes water to flow out at D.

This process will continue as long as both ends of tube are ___________ the water level

6. Pouring our condensed milk from its can The presence of a second hole is to enable _____ to flow into the can. This results in the pressure of air in the can _______ as the atmospheric pressure. The atmospheric pressure will ___________ the milk out of the lower hole.


Explain why the ‘Malaysia Boleh’ sticker sticks well to the helmet when on the surface of the Earth but falls off from the same helmet when the astronaut stands on the surface of the Moon.

Atmospheric Pressure Measuring Instrument

1. Mercury Barometer

Question 1

At sea level: Atmospheric pressure = ………………….. Pa = ……………….. cm Hg

The barometer is made by filling a long glass tube with mercury. The tube is then turned upside down in a bow of mercury. The mercury level in the tube will drop until a level h = 76 cm above the mercury level in the bowl. (a) Why the level does not drop further?

_______________________________________

(b) Pressure at A is due to the ________________

(c) Pressure at B is due to the _________________

(d) Pressure at C = ____

(e) Compare the pressure at A and B.

PA PB

Atmospheric pressure ______ Mercury Pressure (f) If the density of the mercury is 1.36 x 104 kg m-3

and the acceleration due to gravity is 10 ms-2, calculate the atmospheric pressure in pascal.


= ………………. m water = …………. Atm

(g) What is the value of the atmospheric pressure in cm Hg?

(h) What is the pressure at point x in cm Hg? (i) The density of water is 1000 kg m-3. If a

barometer is made using water instead of mercury, and a very long tube, how high is the water column.

Question 2 If a mercury barometer were carried up a mountain, how would you expect the height of the mercury column to change? Explain.

Question 3 The diagram shows a mercury barometer. Gas X is trapped in a glass tube. If the vertical height of the mercury level is 40 cm of Hg and the atmospheric pressure is 75 cm Hg, calculate the pressure exerted by the gas X inside the tube.

2. Aneroid Barometer

An aneroid barometer consists of a flexible metal can which most of the air inside the can has been taken out of it. When the surrounding pressure _________, the top of the can is squeezed down slightly causing the pointer to move along the curved scale measuring the corresponding pressure.


Instruments for Measuring Gas Pressure and Atmospheric Pressure 1. Bourdon Gauge

The movement of a gas into the hollow copper tube causes it to straighten slightly. A system of lever and gear will enable a pointer to move along the round scale indicating the pressure of the gas measured.

2. Manometer

A manometer consists of a U-tube that is filled with a liquid like water, oil or mercury. In figure (a) when both ends of the tube is exposed to __________ pressure, both levels are the same. In figure (b) when one end is connected to a gas supply, the difference in level, h gives the pressure of the gas, P. (a) What is the total pressure a point W? (b) Compare the pressure at W and the

gas pressure.

(c) Write an equation that relate between Patmopherice , Pmercury and Pgas.

Question 1


Show the direction of Pgas , Patmospheric and Pmecury. Given Patmospheric = 76 cm Hg dan h = 20 cm, find the value of Pgas

Pgas = ………………

Pgas = …………………

Pgas = ………………

Question 2

A mercury manometer with one end attached to a gas supply measures a difference in the level of mercury of 32 cm. Calculate the pressure of the gas supply in

(a) cm Hg (b) pascal

[Patmospheric = 76 cm Hg, g = 10 Nkg-1 density of mercury = 1.36 x 104 kg m-3]

TUTORIAL 3.3

1. Gas pressure exits because the gas molecules A. move randomly and freely B. move at the same velocity

C. collide with one another in elastic collisions and with the walls of the container in

D. collides with the wall of the container produces change of momentum


2. Which one of the following pairs of measuring instruments to measure gas pressure is true? A. Bourdon gauge and

manometer B. Manometer and Fortin’s

barometer C. Bourdon gauge and Fortin’

barometer D. Fortin’s barometer Fortin and

Aneroid barometer 3. The figure shows a manometer

used to determine pressure in a gas tank.

Which comparison is correct

about pressure in the gas tank with the atmospheric pressure? (2004) A Pressure in the gas tank is

equal to the atmospheric pressure

B Pressure in the gas tank is greater than the atmospheric pressure

C Pressure in the gas tank is less than the atmospheric pressure

4. The figure shows a manometer is connected to a gas supply.

If the atmospheric pressure is 76 cm Hg determine the pressure of the gas. A 30 cm Hg B 46 cm Hg C 76 cm Hg D 106 cm Hg

5. We do not experience the

atmospheric pressure at sea level because A. the atmospheric is very light B. the density of atmospheric is

less than the density of our body

C. the force exerted by the atmospheric pressure is zero

D. the pressure of our body equal to the atmospheric pressure

6. The figures show a simple

mercury barometer. Which one shows the height, h, to be measure to find atmospheric pressure?

7. The figure shows a mercury

barometer.


What happen to the height of h if the glass tube is tilted ? A decreases B increases C remains unchanged

8. Normally mercury is used in a

barometer because it is A expands uniformly B has a higher density C has a higher boiling point D does not stick to the glass tube 9. The figure shows a suction pump

being pressed against a smooth wall. The pump sticks to the wall when released.

The pump sticks to the wall

because …. (2005) A the atmospheric pressure is

equal to the pressure inside the pump

B the atmospheric pressure is less than the pressure inside the pump

C the atmospheric pressure is more than the pressure inside the pump

10. A suction pump is pulled upwards

to remove dirt from a blocked sink pipe. Which diagram shows the pressures correctly? (2008)

11. The figure shows a mercury

barometer.

What is the pressure at point X? [ The atmospheric pressure = 75 cm Hg ]

A 0 cm Hg B 65 cm Hg C 75cm Hg D 85 cm Hg

E 100 cm Hg 12. The figure shows a mercury

barometer.


If the vacuum space in the tube is filled with gas X , what is the pressure of gas X? [ The atmospheric pressure = 75 cm Hg ] A 0 cm Hg B 20 cm Hg C 55 cm Hg D 75 cm Hg

E 95 cm Hg 13. Diagram below shows a simple

barometer. The difference in height of the two mercury levels is h.

What happens to the value of h when mercury is added to the container? (2007) A. Increases B. Decreases C. No change

14. Which of the following situations

only occurs due to atmospheric pressure? (2007)

15. Diagram 10 shows a manometer connected to a balloon.

Diagram 10

What is the pressure, PB, inside the balloon? (ρ = density of mercury, g = gravitational acceleration, Patm = atmospheric pressure) A. PB = hρg B. PB = Patm – hρg C. PB = Patm - hρg

17. The figure shows an

arrangement of apparatus is used to determine the atmospheric pressure in a laboratory. The length of the glass tube is 100 cm and the atmospheric pressure in the lab is 75 cm Hg.


(a) Name the apparatus as shown in the figure.

……………………………………

(b) Name the space P.

……………………………………

(c)(i) What is the value of h? ………………………………………

(ii) Give one reason why

don’t the mercury column drops until it reaches the level of the mercury in the dish?

……………………………… ………………………………

(d) Determine the pressure in units cm Hg at point

(i) J

(ii) K (e) What will happen to the value of h

if (i) the tube is raised through a

height 10 cm

………………………………

(ii) the tube is lowered through a depth of 5 cm

…………………………….

(iii) the glass tube is inclined about

50 from the vertical line.

………………………………

(iv) the surrounding temperature increases. ………………………………

(v) the apparatus is placed on the top of a mountain. ………………………………

(vi) the space P in the tube is filled with the little of water. ………………………………

3. (a) Why does the pressure in a

plane cabin which fly at a high altitude must be maintained at the atmospheric pressure at the sea level?

……………………………………. …………………………………….

(b) What will happen if one of the plane wind screen broke suddenly? Explain your answer. ……………………………………. ……………………………………. …………………………………….

Documents

3.3 Atmospheric and Gas Pressure 2012