understanding gas pressure 1

HYE THERE!! HOW ARE YOU TODAY?SEEN THAT YOU

LOOK NOT INTERESTED…WHY

NOT WE DO AN EXERCISE FOR A FEW MINUTES?

GOOD MORNING

EVERYONE!

Lets think Lets think togethertogether

Lets think Lets think togethertogether

DO YOU KNOW WHAT TOPIC WE WANT TO

LEARN TODAY?

HMM…I THINK I KNOW. BUT, I’M NOT SURE

UNDERSTANDINUNDERSTANDING GAS G GAS

PRESSUREPRESSURE

Gas particles colliding produce a pressure.

•When the molecules bounce When the molecules bounce off the container walls,off the container walls,they exerts an average they exerts an average force on the walls.force on the walls.•The Force is known as aThe Force is known as a Gas PressureGas Pressure

P = F AP - gas pressureF – force of moleculesA – area surfaces

•Gas Pressure is Gas Pressure is the the force force exerted on a surface exerted on a surface

by air molecules per unit by air molecules per unit areaarea of the surface of the surface

Kinetic TheoryKinetic Theory of Gas of Gas for three for three properties properties

VOLUME

TEMPERATURE

PRESSURE

• A can of gas contains many A can of gas contains many billions of particles. billions of particles.

• Each of them bumps into the walls Each of them bumps into the walls thousands of times every second. thousands of times every second.

• Although we can’t feel each Although we can’t feel each individual bump, they average out individual bump, they average out to produce a constant pressure on to produce a constant pressure on the walls.the walls.

Lets do some Lets do some activity…….activity…….

•Fill a glass with water until it is Fill a glass with water until it is almost full.almost full.

•Place a manila card over the Place a manila card over the glass.glass.

•By supporting the manila card on By supporting the manila card on the top of the glass, slowly invert the top of the glass, slowly invert the glass.the glass.

•Slowly remove the hand which is Slowly remove the hand which is supporting the manila cardsupporting the manila card..

A Simple Experiments…A Simple Experiments…

The answer is..The answer is..

•The atmospheric pressure The atmospheric pressure that presses the manila card that presses the manila card against the glass produce against the glass produce force that is strong enough force that is strong enough to support the weight of the to support the weight of the water in the glass.water in the glass.

ATMOSPHERIC ATMOSPHERIC PRESSUREPRESSURE

Atmospheric Pressure

force exerted by the weight of the air

Atmospheric pressure is defined as the force per unit area exerted against a surface by the weight of the air above that surface

The Pressure caused by the weight of the thick of air above the earth’s surface.

DEFINITION :

The atmosphericThe atmospheric

pressure at sea level pressure at sea level

is 1 atm = 10is 1 atm = 1055 Pa Pa

Atmospheric Atmospheric Pressure Pressure decreases with decreases with altitude.altitude.

Characteristic Characteristic of of

Atmospheric Atmospheric PressurePressure

The atmospheric pressure pushes in all directions

• Give one examples of application of atmospheric pressure in daily life

GAS PRESSURE & ATMOSPHERIC PRESSURE

GAS PRESSURE & ATMOSPHERIC PRESSURE

Gas pressure based on theKinetic theory of gases

Gas pressure based on theKinetic theory of gases

Atmospheric pressure in termsOf the weight of the atmosphereAtmospheric pressure in terms

Of the weight of the atmosphere

Atmospheric pressure at sea level= 105Nm-2 or 105 Pa=760 mm Hg

Atmospheric pressure at sea level= 105Nm-2 or 105 Pa=760 mm Hg

Gas Pressure is Gas Pressure is the the forceforceexerted on a surface exerted on a surface by air molecules perby air molecules per

unit unit areaarea of the surface of the surface

Gas Pressure is Gas Pressure is the the forceforceexerted on a surface exerted on a surface by air molecules perby air molecules per

unit unit areaarea of the surface of the surfacea) Rubber sucker b) strawsc) Syringes d) siphons

e) Lift pumps

a) Rubber sucker b) strawsc) Syringes d) siphons

e) Lift pumps

• In the atmosphere, the force that In the atmosphere, the force that compresses the air at the surface is compresses the air at the surface is just the weight of all the air in the just the weight of all the air in the atmospheric column above itatmospheric column above it

• At the surface the atmospheric At the surface the atmospheric pressure is on average P0 = 101.3 kPa pressure is on average P0 = 101.3 kPa = 1013 mb= 1013 mb

Fortin Barometers Fortin Barometers

• In the Fortin barometer, the level of mercury in the glass at In the Fortin barometer, the level of mercury in the glass at the bottom of the barometer cistern is adjusted to a scale the bottom of the barometer cistern is adjusted to a scale zero, known as the fiducial point, each time a reading is to zero, known as the fiducial point, each time a reading is to be taken. The level of mercury in the column is then read be taken. The level of mercury in the column is then read against the scale, using a vernier adjustment for extra against the scale, using a vernier adjustment for extra accuracy. accuracy.

In addition to instruments manufactured under the Russell In addition to instruments manufactured under the Russell Scientific Instruments name, we manufacture, service and Scientific Instruments name, we manufacture, service and repair F Darton and WF Stanley, Griffin and George and repair F Darton and WF Stanley, Griffin and George and Gallenkamp precision mercury barometers.Gallenkamp precision mercury barometers.

Please note that all precision barometers are supplied in a Please note that all precision barometers are supplied in a purpose-built fibreboard case with a polystyrene cutout purpose-built fibreboard case with a polystyrene cutout inner to support the instrument.inner to support the instrument.

Aneroid barometer. Aneroid barometer.