Pascal's Law is an important law in atmospheric
physics. The law states that fluids (including gases such
as Earths atmosphere) transmit pressure in all
directions. Therefore, the pressure of the atmosphere is
exerted not only downward on the surface of an object,
but also in all directions against a surface that is
exposed to the atmosphere.
What is the definition of pressure?
With a sea level pressure reading of 1000 mb,
what would be the approximate pressure at
What environmental changes have the biggest
effect on pressure changes?
LEARNING OBJECTIVE: Describe how
temperature is measured and determine how
the atmosphere is affected by temperature.
Temperature is the measure of molecular motion.
Its intensity is determined from absolute zero (Kelvin
scale), the point which all molecular motion stops.
Temperature is the degree of hotness or coldness, or it
may be considered as a measure of heat intensity.
Long ago it was recognized that uniformity in the
measurement of temperature was essential. It would be
unwise to rely on such subjective judgments of
temperature as cool, cooler, and coolest; therefore,
arbitrary scales were devised. Some of them are
described in this section. They are Fahrenheit, Celsius,
and absolute (Kelvin) scales. These are the scales used
by the meteorological services of all the countries in the
world. Table 1-2 shows a temperature conversion scale
for Celsius, Fahrenheit, and Kelvin.
Gabriel Daniel Fahrenheit invented the Fahrenheit
scale about 1710. He was the first to use mercury in a
thermometer. The Fahrenheit scale has 180 divisions or
degrees between the freezing (32°F) and boiling
(212°F) points of water.
Anders Celsius devised the Celsius scale during the
18th century. This scale has reference points with
respect to water of 0°C for freezing and 100°C for
boiling. It should be noted that many publications still
refer to the centigrade temperature scale. Centigrade
simply means graduated in 100 increments, and has
recently and officially adopted the name of its
Absolute Scale (Kelvin)
Another scale in wide use by scientists in many
fields is the absolute scale or Kelvin scale, developed
by Lord Kelvin of England. On this scale the freezing
point of water is 273°K and the boiling point of water is
373°K. The absolute zero value is considered to be a
point at which theoretically no molecular activity
exists. This places the absolute zero at a minus 2730 on
the Celsius scale, since the degree divisions are equal in
size on both scales. The absolute zero value on the
Fahrenheit scale falls at minus 459.6°F.
Two scales, Fahrenheit and Celsius, are commonly
used. With the Celsius and Fahrenheit scales, it is often
necessary to change the temperature value of one scale
to that of the other. Generally a temperature conversion
table, like table 1-2, is used or a temperature computer.
If these are not available, you must then use one of the
following mathematical methods to convert one scale to
It is important to note that there are 100 divisions
between the freezing and boiling points of water on the
Celsius scale. There are 180 divisions between the
same references on the Fahrenheit scale. Therefore, one
degree on the Celsius scale equals nine-fifths degree on
the Fahrenheit scale. In converting Fahrenheit values to
Celsius values the formula is:
In converting Celsius values to Fahrenheit values the