2. DOYOU STILL REMEMBER?
• Define Pressure as N/m2
• Explain why pressure depends upon
surface area
• Calculate Pressure given relevant
data
• Justify how pressure is affected by
car tyres
Why would a lady in high heels standing on your foot hurt
more than an elephant standing on your foot?
4. DOESTHE AIR HAS MASS?
• Click the link to confirm
whether air has mass or not
• https://youtu.be/
8vK5ksK4wFs?t=62
• Now, write in note book of
what you see and what you
learn. You can also draw
and label the diagram of
the activity.
Is that true? Do
you believe that
air has mass?
AIR AIR
5. SO NOW WE KNOW THAT AIR HAS
MASS & WEIGHT, HOW THAT
RELATES TO AIR PRESSURE?
Can you feel the
air pressure?
6. AIR PRESSURE
• Air pressure is the measure of the force which air
molecules push on a surface.
• Air Pressure is GREATEST at the surface of the Earth
because there is more of the atmosphere above you
to push down on you.
7. • As you move UP through the atmosphere, air
pressure decreases.
Graph of altitude against air pressure
What do you understand from the graph? Write in
your notes.
8. AIR PRESSURE IS DEPENDANT ON
DENSITY
• More dense air will have a higher air pressure-
there are more air molecules in a given space to push
down on you
• Less dense air will have a lower air pressure-
there are fewer air molecules to push down on you.
More Dense= more particles to
push down on you
Less Dense= fewer particles to
push down on you
9. AIR PRESSURE IS AFFECTED BY 3
FACTORS
• 1- Elevation, or altitude
• 2- Temperature
• 3- Humidity/ Water content
10. The people at the bottom of the pyramid can feel all the
weight and pressure of the people on top (high pressure).
The person on the top doesn’t feel any weight (less
pressure).
11. IMPACT OF ELEVATION ON AIR
PRESSURE
• As you move up through the atmosphere, air
pressure decreases.
– There are fewer air molecules above you to push down on
you, so the force of the air will be less.
12. Observe and compare the no. of particles ‘above’ the guy at
the top to the guy at the sea level (bottom)
13. IMPACT OF TEMPERATURE ON AIR
PRESSURE
• Warm air is less dense than cold air.
Therefore, warm air has a lower air pressure
and cold air has a higher air pressure.
– The molecules in warm air are moving fast and
are spread farther apart. Therefore there are
fewer air molecules in a given area to push down on
you.
Warm Air Cold Air
14. Could Air Crush a Metal Tank Car ?????
The inside of this tank car was washed out and cleaned with HOT
steam. Then all the outlet valves were shut . The tank car was
sealed. All the workers went home for the evening.
In the morning when they returned this is what they found.
This tank car was smashed, crushed, or collapsed by an unseen
force why?
15. IMPACT OF WATER CONTENT OR
HUMIDITY, ON AIR PRESSURE
• Moist air is less dense than dry air, and therefore
has a lower air pressure.
• A water molecule has less mass than other
molecules that make up the air. If you replace some
of the air molecules with water molecules, the water
lowers the density (and lowers the air pressure)
O N
O N
H2O
O H2O
N
Weighs less since
H2O is lighter than
Nitrogen and
Oxygen
16. As altitude
increases . .
Air
pressure
As temperature
increases . .
As humidity
increases . .
Air
pressure
Air
pressure
decreases decreases decreases
17. How do you measure air
pressure and atmospheric
pressure?
18. BAROMETER
• The piece of equipment used to measure air
pressure is a Barometer
Aneroid Barometer Mercury Barometer
19. h
Notice that above A,
is vacuum!
Will the value of h change if
The vacuum part is filled
With air? Discuss
20. AIR PRESSURE AFFECTS THE WEATHER
• Air pressure in a weather system reflects the
amount of water in the air, which affects the
weather.
Low air pressure
usually results in Bad
weather: stormy,
cloudy, overcast.
High air pressure
usually results in
Good weather: clear
skies, no precipitation
