Page 13 - Air and gas Drilling Field Guide 3rd Edition

1.2 Engineering Calculations and Units 3

These reference weights and measures are kept in Paris, France, for all nations
and other entities to utilize. Since 1875 the SI units system has gained rapid
and widespread use throughout the world. This system is characterized by its
consistent set of units and simplicity of use. SI units are based on multiples of dec-
ades or units of tens. All basic weights and measurement units within SI are in
increasing magnitudes of multiples of 10, 100, 1000, etc. Nearly all other unit sys-
tems in use in international trade and commerce around the world today must be
referenced against the SI standard units before they are considered legitimate for
legal matters or for international commercial trade.

1.2.1 Physical Mechanics
There are important fundamental definitions of units that must be used to define
any units system. These are as follow:

Force is the action of one body on another that causes acceleration of the
second body unless acted on by an equal and opposite action countering
the effect of the first body.
Time is a measure of the sequence of events. In Newtonian mechanics, time is an
absolute quantity. In relativistic mechanics, it is relative to the frame of
reference in which the sequence of events is observed. The common unit of
time is seconds.
Inertia is that property of matter that causes a resistance to any change in the
motion of a body.
Mass is a quantitative measure of inertia.
This monograph deals exclusively with Newtonian mechanics. Newton’s gen-
eral laws are as follow:
Law I. If a balanced force system acts on a particle at rest, it will remain at
rest. If a balanced force system acts on a particle in motion, it will remain
in motion in a straight line without acceleration.
Law II. If an unbalanced force system acts on a particle, it will accelerate in
proportion to the magnitude and in the direction of the resultant force.
Law III. When two particles exert forces on each other, these forces are equal
in magnitude, opposite in direction, and collinear.
Note that the aforementioned original definitions of the just-defined laws by
Newton were conceived around the concept of force.

1.2.2 Basic Units and Usage
The USCS is a gravitational system, as its units of length, force, and time (i.e.,
L, F, and T, respectively) are considered fundamental dimensions of the system
and all other units, including mass, are derived. The SI is an absolute system,
as its units of length, mass, and time (i.e., L, M, and T, respectively) are