Understanding Gas Pressure 1

GOOD MORNING EVERYONE!

HYE THERE!! HOW ARE YOU TODAY?SEEN THAT YOU LOOK NOT INTERESTED…WHY NOT WE DO AN EXERCISE FOR A FEW MINUTES?

Lets think Lets think together together

DO YOU KNOW WHAT TOPIC WE WANT TO LEARN TODAY?

HMM…I THINK I KNOW. BUT, I’M NOT SURE

UNDERSTANDING GAS PRESSURE

•When the molecules bounce

off the container walls, they exerts an average force on the walls. The Force is known as a • Gas particles colliding produce a pressure. Gas Pressure

P = F A

P - gas pressure F – force of molecules A – area surfaces •Gas Pressure is the force exerted on a surface by air molecules per unit area of the surface

Kinetic Theory of Gas for three properties

VOLUME

PRESSURE TEMPERATURE

• A can of gas contains many

billions of particles. • Each of them bumps into the walls thousands of times every second. • Although we can’t feel each individual bump, they average out to produce a constant pressure on the walls.

Lets do some activity…….

A Simple Experiments… • Fill a glass with water until it is

almost full. • Place a manila card over the glass. • By supporting the manila card on the top of the glass, slowly invert the glass. • Slowly remove the hand which is supporting the manila card.

The answer is.. • The atmospheric pressure

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

ATMOSPHERIC PRESSURE

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

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

The atmospheric pressure pushes in all directions

Characteristic of Atmospheric Pressure

The atmospheric pressure at sea level is 1 atm = 105 Pa

Atmospheric Pressure decreases with altitude.

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

GAS PRESSURE & ATMOSPHERIC PRESSURE Gas pressure based on the Kinetic theory of gases

Gas Pressure is the force exerted on a surface by air molecules per unit area of the surface

Atmospheric pressure in terms Of the weight of the atmosphere Atmospheric pressure at sea level = 105Nm-2 or 105 Pa =760 mm Hg

a) Rubber sucker c) Syringes e) Lift pumps

b) straws d) siphons

• In the atmosphere, the force that

compresses the air at the surface is just the weight of all the air in the atmospheric column above it

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

Fortin Barometers • In the Fortin barometer, the level of mercury in the glass at the bottom of the barometer cistern is adjusted to a scale zero, known as the fiducial point, each time a reading is to be taken. The level of mercury in the column is then read against the scale, using a vernier adjustment for extra accuracy. In addition to instruments manufactured under the Russell Scientific Instruments name, we manufacture, service and repair F Darton and WF Stanley, Griffin and George and Gallenkamp precision mercury barometers. Please note that all precision barometers are supplied in a purpose-built fibreboard case with a polystyrene cutout inner to support the instrument.

Aneroid barometer.