# 7th Atmosphere Atmosphere Key Terms Density

```7th Atmosphere
Atmosphere
Key Terms
1. Density- The amount of matter in a given volume or area. Density is also described as a
measure of compactness of matter. It is determined by dividing the amount of mass of a
substance by its volume. D=m/v
2. Atmosphere- the thin layer of gases that surround the Earth. It is held in place by the
force of the Earth’s gravity.
3. Charles Law- The law that describes the relationship between the temperature and the
volume of a gas under the conditions in which the pressure and amount of a gas is
constant. Charles’s Law states that the volume of a given amount of dry ideal gas is
directly proportional to the Kelvin Temperature. Charles’ Law can be represented by the
formula:
a. V₁ / T₁ = V₂ / T₂
4. Troposphere- the layer of the atmosphere extends from the surface of the Earth to
approximately ten to twelve kilometers above the Earth’s surface. It is the layer in which
most of the Earth’s weather occurs.
5. Stratosphere- The layer of the atmosphere that extends from the top of the troposphere
to about 50 km above Earth’s surface. It is the layer where most clouds are formed.
Stratosphere contains Ozone, which traps heat and warms the surrounding air.
6. Mesosphere- located above the stratosphere and much cooler, Begins 50 km above
Earth’s surface and ends at 80 km. Most meteoroids burn up in the mesosphere,
producing meteor trails.
7. Thermosphere- The outermost layer of the atmosphere. Extends from 80 km above
Earth’s surface outward into space. Gas atoms and molecules there are so far apart that
the air blends gradually into outer space. Even though the air in the thermosphere is thin,
it is very hot, up to 1,800&deg;C.
8. Exosphere- The outer most layer of the thermosphere. The exosphere extends from 550
km outward for thousands of kilometers. Satellites orbit in the exosphere making it
possible for you to make a long distance phone call or watch television.
9. Atmospheric Pressure- the sum of forces exerted on the surface of the Earth by the
molecules that compose the atmosphere per unit area. Atmospheric pressure can be
represented by the following equation and is measured in units of millibars:
a. P = ∑ F / A
∑ F = the sum of forces exerted by molecules of the atmosphere
A = area
10. Barometric Pressure- An indication of the atmospheric pressure in an area as measure
in millimeters of mercury (mm Hg) with a barometer. The pressure in mm Hg can be
converted to millibars using the equation :
a. P in mm Hg / 0.750062
7th Atmosphere
11. High Pressure System- when the atmospheric pressure at one area of the Earth is higher
than the area areas that surround it.
12. Low Pressure System- when the atmospheric pressure at one area of the Earth is lower
than the areas that surround it.
13. Air Mass- a large body of air that possess certain temperature and humidity
14. Front- The boundary between air masses of different densities
15. Cold Front- The boundary between a cold air mass and a warm air mass. In a Cold
Front, the colder air moves in behind the cooler air mass
16. Warm Front- The boundary between a cold air mass and a warm air mass. In a Warm
Front, the warmer air mass moves in behind the cooler air mass.
17. Wind- Horizontal movements of air set into motion by pressure differences that exist
within the Earth’s atmosphere
18. Pressure Gradient Force (PGF)- The difference in pressure between higher and lower
areas of pressure and the distance between the two areas.
a. PGF = area of higher pressure (mb) – area of lower pressure (mb)
distance between areas of pressure (km)
19. Isobar- Lines on weather or atmospheric pressure map that indicate areas of equal
atmospheric pressure
20. Barometer- One of the key instruments used by meteorologist to measure changes in the
atmospheric pressure. Changes in atmospheric pressure measured with a mercury
barometer are reported in millimeters of mercury (mm Hg)
21. Evaporation- a change of phase in which the liquid phase of a substance is converted to
its gaseous phase
22. Condensation- a change of phase in which the gaseous phase of a substance is converted
to its liquid phase
23. Precipitation- Liquid and solid phases of water that fall from the sky. Precipitation
includes rain, hail, snow, freezing rain, and sleet.
24. Meteorology- The study of the atmosphere and its associated phenomena
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