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Notes on Air Pressure
Pages 10-14 Weather
Air has mass therefore it also has:
- Density: The amount of mass in a
given volume is density
- Pressure: The force pushing down
on a surface is pressure
Air Pressure: The
weight of a column of air pressing down on an area of Earth.
atmosphere is heavy, as heavy as a school bus!
reason it doesn’t crush you is that it is spread out and pushes equally in
substances have more mass so they add more pressure, therefore
air exerts more pressure than less dense air.
instrument that measures air pressure.
- Mercury Barometer: Mercury is
filled in a glass dish and in a long columnar tube. When air pressure increases it pushes
down on the mercury in the dish, forcing it up into the tube.
- Aneroid Barometer: Aneroid means without liquid. It has an airtight
chamber. When air pressure
increases the chamber walls are pushed in.
The needle in the dial indicates the change in pressure.
- Normal Air pressure at sea level
is 76 cm or about 30 inches
- Units of Air pressure:
- Inches or centimeters
- Millibars – 1 inch = 30 millibars
so sea level would be about 2280 millibars
Altitude and its
effect on air pressure and density:
pressure decreases as altitude increases – The higher up you go the less
air is pushing down on you.
pressure decreases, density decreases.
The higher up you go the less dense the air is – The molecules of air
are further apart. This means that the
amount of oxygen in a given space is less, so you would have trouble breathing.