Page 152 - Standard Handbook Of Petroleum & Natural Gas Engineering

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General Engineering and Science

BASIC MECHANICS (STATICS AND DYNAMICS)
Mechanics is the physical science that deals with the effects of forces on the state
of motion or rest of solid, liquid, or gaseous bodies. The field may be divided into
the mechanics of rigid bodies, the mechanics of deformable bodies, and the mechanics
of fluids.
A rigid body is one that does not deform. True rigid bodies do not exist in nature;
however, the assumption of rigid body behavior is usually an acceptable accurate
simplification for examining the state of motion or rest of structures and elements of
structures. The rigid body assumption is not useful in the study of structural failure.
Rigid body mechanics is further subdivided into the study of bodies at rest, statics,
and the study of bodies in motion, dynamics.

Definitions, Laws, and Units
Fundamental Quantities

All of Newtonian mechanics is developed from the independent and absolute
concepts ofspace, time, and mass. These quantities cannot be exactly defined, but they
may be functionally defined as follows:
Space. Some fixed reference system in which the position of a body can be uniquely
defined. The concept of space is generally handled by imposition of a coordinate
system, such as the Cartesian system, in which the position of a body can be stated
mathematically.
Time. Physical events generally occur in some causal sequence. Time is a measure
of this sequence and is required in addition to position in space in order to fully
specify an event.
Muss. A measure of the resistance of a body to changes in its state of motion.

Derived Quantities
The concepts of space, time, and mass may be combined to produce additional
useful measures and concepts.
Particle. An entity which has mass, but can be considered to occupy a point in
space. Rigid bodies that are not subject to the action of an unbalanced couple often
may be treated as particles.
Body. A collection of particles. A rigid body is a rigidly connected collection of
particles.
Force. The action of one body on another. This action will cause a change in the
motion of the first body unless counteracted by an additional force or forces. A force
may be produced either by actual contact or remotely (gravitation, electrostatics,
magnetism, etc.). Force is a vector quantity.
Couple. If two forces of equal magnitude, opposite direction, and different lines of
action act on a body, they produce a tendency for rotation, but no tendency for
translation. Such a pair of forces is called a couple. The magnitude of the moment

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