The conventional unit of weight in the metric
system is the gram (gm). You could use table 1-1 and
substitute the word gram for meter and the symbol (gm)
for the symbol (M). You would then have a table for
metric weight. The gram is the weight of 1 cm3 of pure
water at 4°C. At this point it may be useful to compare
the weight of an object to its mass. The weight of the 1
cm3 of water is 1 gin. Weight and mass are proportional
to each other. However, the weight of the 1 cm3 of water
changes as you move away from the gravitational
center of Earth. In space the 1 cm3 of water is
weightless, but it is still a mass. Mass is expressed as a
function of inertia/acceleration, while weight is a
function of gravitational force. When we express the
movement of an object we use the terms mass and
Time is measured in hours, minutes, and seconds in
both systems. Hence, the second need not be explained
in the CGS system. With knowledge of how the CGS
system can be used to express physical entities, you
now have all the background to express such things as
density and force.
With the previous explanation of grams and
centimeters, you should be able to understand how
physical factors can be measured and described. For
example, density is the weight something has per unit
of volume. The density of water is given as 1 gram per
cubic centimeter or 1 gm/cm.
By comparison, the
density of water in the English system is 62.4 pounds
per cubic foot or 62.4 lb/ft3.
Force is measured in dynes. A dyne is the force that
moves a mass of 1 gram, 1 centimeter per square
second. This is commonly written as gin cm per sec2,
gin cm/sec/sec or gm/cm/sec2. The force necessary for
a gram to be accelerated at 980.665 cm/sec2 at 45°
latitude is 980.665 dynes. For more detailed conversion
Q1-1. What units does the metric (CGS) system
Q1-2. What is the difference between weight and
What does a dyne measure?
radiation and insolation are affected by the
The Sun is a great thermonuclear reactor about 93
million miles from Earth. It is the original source of
energy for the atmosphere and life itself. The Suns
energy is efficiently stored on Earth in such things as
oil, coal, and wood. Each of these was produced by
some biological means when the Sun acted upon living
organisms. Our existence depends on the Sun because
without the Sun there would be no warmth on Earth, no
plants to feed animal life, and no animal life to feed
The Sun is important in meteorology because all
natural phenomena can be traced, directly or indirectly,
to the energy received from the Sun. Although the Sun
radiates its energy in all directions, only a small portion
reaches our atmosphere. This relatively small portion of
the Suns total energy represents a large portion of the
heat energy for our Earth. It is of such importance in
meteorology that every Aerographers Mate should
have at least a basic knowledge about the Sun and the
effects it has on Earths weather.
The Sun may be regarded as the only source of heat
energy that is supplied to earths surface and the
atmosphere. All weather and motions in the atmosphere
are due to the energy radiated from the Sun.
The Suns core has a temperature of 15,000,000°K
and a surface temperature of about 6,000°K (10,300°F).
The Sun radiates electromagnetic energy in all
directions. However, Earth intercepts only a small
fraction of this energy. Most of the electromagnetic
energy radiated by the Sun is in the form of light waves.
Only a tiny fraction is in the form of heat waves. Even
so, better than 99.9 percent of Earths heat is derived
from the Sun in the form of radiant energy.