Transcript Air Pressure and Wind Chapter 19

Aim: What is
Pressure and what
does it make?
Do Now: Define
Pressure. Give an
example of
pressure change
from an
experience you
had.
I. Air Pressure
- the pressure exerted by the weight of air
(molecules)
II. Causes of Air Pressure
-
Differences in
temperature cause
differences in air
pressure.
-
temperature changes
the density of the air.
-
Water vapor changes
the density.
Warm
Cold
A. Cold air
- contracts (more dense)
- sinks
- creates more pressure
B. Warm air
- expands (less dense)
- rises
- creates less pressure
III. Measuring Air
Pressure
- air pressure is
measured by using a
barometer.
- As pressure increases
the liquid in the
barometer rises.
- As pressure decreases
the liquid lowers in
the barometer.
** A decreasing barometer (air is rising and
pressure is low) means the weather will be
cloudy and wet. (water vapor is less dense)
** An increasing barometer (air is sinking and
pressure is high) means the weather will be dry
and sunny.
IV. Pressure gradient:
- describes the
difference in air pressure
seen on a map. Drawn
using isobars.
- This difference creates
wind. Air moves from high
pressure areas to low
pressure areas (H L).
V. Winds
- The movement of air due to differences in air
pressure
- Closely spaced isobars create a strong pressure gradient
& high winds (steep gradient)
- Widely spaced isobars create a weak pressure gradient
& light winds (gentle gradient)
Barometric Pressure Reading for April 10th 2013 (Wednesday)
High pressure =
happy weather
(rising barometer)
Using the chart above,
describe; 1) how the chart
shows the weather was
nice all during the day? 2)
how the chart shows the
weather was bad all during
the night? 3) What
changed in the air?
Low pressure =
lousy weather (falling
barometer)
1) Pressure was rising from 7am
to 1pm.
2) Pressure was falling from 5pm
to 10pm.
3) More water vapor was entering
the air, making the pressure
decrease and causing lousy
weather.
Closure:
From the back table,
take the worksheet on
pressure and complete
this working with your
partner.