Air has mass therefore it
- 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.
- The atmosphere is
heavy, as heavy as a school bus!
- The reason it doesn’t
crush you is that it is spread out and pushes equally in all directions
- Denser substances
have more mass so they add more pressure, therefore
- Denser 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
- Inches or
- Millibars – 1
inch = 30 millibars so sea level would be about 2280 millibars
Altitude and its effect
on air pressure and density:
The higher up you go the less air is pushing down on you.
As air pressure 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.