terms. The change in position of any portion of matter is
motion. The atmosphere is a gas and is subject to much
motion. Temperature, pressure, and density act to
produce the motions of the atmosphere. These motions
are subject to well-defined physical laws. An
explanation of Newton’s laws of motion can help you to
understand some of the reasons why the atmosphere
moves as it does.
Newton’s First Law
Sir Isaac Newton, a foremost English physicist,
formulated three important laws relative to motion. His
first law, the law of inertia, states, every body continues
in its state of rest or uniform motion in a straight line
unless it is compelled to change by applied forces.”
Although the atmosphere is a mixture of gases and has
physical properties peculiar to gases, it still behaves in
many respects as a body when considered in the terms
of Newton’s law. There would be no movement of great
quantities of air unless there were forces to cause that
movement. For instance, air moves from one area to
another because there is a force (or forces) great enough
to change its direction or to overcome its tendency to
remain at rest.
Newton’s Second Law
Newton’s second law of motion, force, and
acceleration states, “the change of motion of a body is
proportional to the applied force and takes place in the
direction of the straight line in which that force is
applied.” In respect to the atmosphere, this means that a
change of motion in the atmosphere is determined by
the force acting upon it, and that change takes place in
the direction of that applied force.
From Newton’s second law of motion the following
conclusions can be determined:
1.
If different forces are acting upon the same
mass, different accelerations are produced that are
proportional to the forces.
2.
For
different
masses
to
acquire
equal
acceleration by different forces, the forces must be
proportional to the masses.
3.
Equal forces acting upon different masses
produce different accelerations that are proportional to
the masses.
Newton’s Third Law
Newton’s third law of motion states, “to every
action there is always opposed an equal reaction; or, the
mutual actions of two bodies upon each other are
always equal, and directed to contrary parts.” In other
words forces acting on a body originate in other bodies
that make up its environment. Any single force is only
one aspect of a mutual interaction between two bodies.
WORK
Work is done when a force succeeds in overcoming
a body’s inertia and moving the body in the direction
the force is applied. The formula is
W = F × d
where W is work, F is force and d is the distance moved.
The amount of work done is the product of the
magnitude of the force and the distance moved.
Work is measured in the English system by the
foot-pound; that is, if 1 pound of force acts through a
distance of 1 foot, it performs 1 foot-pound of work. In
the metric CGS system, force is measured in dynes,
distance is measured in centimeters, and work is
denoted in ergs. An erg is the work done by a force of
one dyne exerted for a distance of one centimeter.
Another unit used to measure work is the joule. It is
simply 10,000,000 ergs, and is equivalent to just under
three-fourths of a foot-pound.
ENERGY
Energy is defined as the ability to do work. Energy
is conservative, meaning it may be neither created nor
destroyed. It is defined in two forms—potential energy
and kinetic energy. As its name implies, potential
energy is the amount of energy that MAY BE
AVAILABLE to a body due to its position. It is
primarily due to the force of gravity. The higher a body
is raised above the surface, the greater its POTENTIAL
energy. Kinetic energy is the energy available to a body
due to its motion through a field. The total amount of
energy a body possesses is the sum of its potential and
kinetic energies. The total amount of energy available
to a body determines how much work it can
accomplish.
FORCE
There are two types of forces the AG deals
with—contact force and action at a distance force.
Contact force is the force that occurs when pressure is
2-2
