Gas Pressure&Atmospheric Pressure (4sc2)

7/27/2019 Gas Pressure&Atmospheric Pressure (4sc2)

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What will happen when we blow

the air into the balloon car and

released it?

Why the water does not squirts out

into a hole when we close the

mouth of the bottle?

WHY???


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What made the water remain inthe glass and not fall out?

Why doesnt the cupboarddrop?


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FORCE AND PRESSURE

GAS PRESSURE AND

ATMOSPHERIC

PRESSURE


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GAS PRESSURE What do you feel when you squeeze your

finger onto the balloon that fully with air?

What is gas pressure :

Gas pressure is the force per unit areaexerted by the gas particles as they collidewith the walls of their container


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Kinetic Molecular Theory:

Gases are made oftiny, individual particles. Gas particles move rapidly and randomly in

straight-line motion. Particles collide with one

another and walls of the container in elastic

collision

Individual particles are far apart and have very

little attraction for each other. They move

independently

The averge kinetic energies of particles of

different gasses are equal at given temperature

The average kinetic energies of gas particle

increases as the temperature increases


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Atmospheric pressure

1. Atmosphere - several layers of thick air surrounding the

Earth.

2. Atmosphere is most dense at sea level. As we goes higher,

the air becomes less dense.

=> As the altitude increases, the density of air decreases.

3. Atmospheric pressure - pressure exerted by the atmosphere

on the Earths surface and all objects on it.

At sea level, atmospheric pressure = 1.03

105

Pa = pressure of water column of height 10 m.


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Earth.


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MEASURING GASPRESSURE BOURDON

GAUGE

MANOMETER


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Barometer


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If pressure is applied, the copper tube will bestraightened slightly.

The copper tube pushes the lever system andhence rotates the pointer.

Gas pressure can be read directly from the scale.


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The pressure can be measured by calculating the height

between the two columns of liquid

Pgas = Patm + Pliquid

Pgas = Po + hg

Pgas = Gas Pressure( Nm/ Pa)

Patm = Atmospheric Pressure ( 76 cm Hg/ 1.013x105 Pa)g = Gravitational Field Strength (9.8ms)

= density of the liquid used (kgm)

h= height/ length of liquid (cm)


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ATMOSPHERICPRESSURE What is atmospheric pressure:

Atmospheric pressure is the per unit areaexerted against a surface by the weight ofthe air molecules above that surface

Also known as air pressure


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Existence of Atmospheric Pressure

The cardboard does not fall and the water remainsin the glass even though its not supported byanything. Why???

Explanation:

The force caused by the atmospheric pressure actson the surface of the cardboard is greater than theweight of the water in the glass pushing it up andholding up the water in the glass.


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Crumble Can

When a can filled with hot water is closed and

is cooled down rapidly by pouring cold wateron it, it will crash instantly. Why???

Explanation:When the air inside the can is cooled, its

pressure decreases. The high atmosphericpressure outside exerts a great force on the canand causes it crashes.


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Atmo pheric Pressure and Altitude

When we are at the top of a high mountain, we

can face breathing difficulties. Why???

Explanation:Atmospheric pressure decreases as the altitude

increases and we need to breathe more often than

when we are at sea level. The higher you go the

lower is the gas pressure. The air becomes less

dense and the air pressure decreases


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MEASURING ATMOSPHERICPRESSURE SIMPLE

BAROMETER

ANEROID

BAROMETER


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QUESTIONS


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GROUP WORKRUBBER SUCKER SYRINGE

STRAW VACUUM CLEANER


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RUBBER SUCKER

When the sucker is pressed into place, most

of the air behind it is squeezed out.

The sucker is held in position by the pressure

of atmosphere on the outside surface of therubber.

If the seal between the sucker and the

surface is airtight , the sucker will stickpermanently.


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SYRINGE

Pulling up the piston reduces the atmospheric

pressure inside the cylinder.

The atmospheric pressure on the liquid surface then

pushes the liquid up into the syringe. If we then hold the plunger in place and lift the

syringe out of liquid , none will fall out. This is again

due to atmospheric pressure


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STRAW

When we suck through a straw, the air

pressure in the straw is lowered.

Then the pressure of the atmosphere acting

on the surface of the drink in the glass

pushes the water up the straw and into our

mouth.


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VACUUM CLEANER

A vacuum cleaner produces only a partial

vacuum.

The fan inside the cylinder blows air out of

the vents. Which less air inside , the air

pressure there drops.

The atmospheric pressure outside then

pushes air up the cleaner hose, carrying dust

and dirt with it.

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Gas Pressure&Atmospheric Pressure (4sc2)