 2000, W. E. Haisler
Review of General Principles (RS 1, 12)
1
Review of General Principles (RS 1, 12)
What is Mechanics?
 Branch of Physical Sciences dealing with the response
of bodies to the action of forces
 Applies to Gases, Liquids and Solid Bodies
Mechanics is Generally Divided into Three Areas:
1. Statics - Bodies acted upon by balanced forces and hence
are at rest or have uniform motion.
 2000, W. E. Haisler
Review of General Principles (RS 1, 12)
2
2. Kinematics - Concerned with the motion of bodies
without regard to the manner in which the motion is
produced. Sometimes referred to as the geometry of
motion. Provides relationships between motion, velocity,
acceleration, etc. of the points on a body or the motion of
a particle due to physical constraints.
3. Kinetics - Bodies acted upon by unbalanced forces;
hence, they have nonuniform or accelerated motions.
Sometimes called the dynamics problem. Provides
relationships between the motion of a body and the forces
and/or moments acting on the body.
 2000, W. E. Haisler
Review of General Principles (RS 1, 12)
3
Mechanics of Deformable Bodies - The area of Mechanics
that deals with internal force distributions and deformations
developed in engineering structures when subjected to forces
and moments is known as the mechanics of deformable
bodies. Also called mechanics of materials. These topics
are covered in ENGR 214.
Kinetic relationships can be obtained by applying
Conservation of Linear and/or Angular Momentum and/or
Conservation of Energy. Or, equivalently, by Newton's
Laws of Motion.
 2000, W. E. Haisler
Review of General Principles (RS 1, 12)
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Newton's 4 Laws
Law 1: A particle originally at rest will remain at rest; a
particle originally moving with a constant velocity
will continue to move with a constant velocity along
a straight line, unless the particle is acted on by an
unbalanced force.
Law 2: When a particle is acted on by an unbalanced force,
the particle will be accelerated in the direction of the
force; the magnitude of the acceleration will be
directly proportional to the force and inversely
proportional to the mass of the particle.
 2000, W. E. Haisler
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Review of General Principles (RS 1, 12)
Law 3: For every action there is an equal and opposite
reaction. The forces of action and reaction between
contacting bodies are equal in magnitude, opposite
in direction, and collinear.
Law 4: Newton's Law of Gravitation: F  G
m1m2
r2
 2000, W. E. Haisler
Review of General Principles (RS 1, 12)
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Unit Systems
In mechanics, we use quantities such as mass, force, length,
time, velocity, acceleration, etc. when applying conservation
principles or Newton's Laws. We can consider some of
these to be either fundamental or derived quantities.
Fundamental quantities cannot be defined in terms of other
physical quantities. Examples are length and time.
Derived quantities are defined in terms of other physical
quanties. Examples are area, velocity, acceleration, and
pressure.
 2000, W. E. Haisler
Review of General Principles (RS 1, 12)
7
U.S. Customary System (English System)
 Fundamental quantities: length (foot), force (pound) and
time (second).
 Mass (slug) is a derived quantity such that one slug is the
mass that is accelerated one foot per second squared by a
force of one pound, i.e.,
1 slug = 1 lbf / (1 ft/s2) = 1 lbf s2/ft.
Internation System of Units (SI)
 Fundamental quantities: length (meter), mass (kg) and
time (second).
 Force (Newton) is a derived quantity such that one Newton
is the force required to give one kg of mass an acceleration
of one meter per second squared, i.e.,
1 Newton = 1 kg (1 m/s2) = 1 kg m/s2.
 2000, W. E. Haisler
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Review of General Principles (RS 1, 12)
Some Derived Units and their Names/Symbols
Force
Pressure or stress
Energy or work
F
F / L2
FL
kgm / s
N / m2
Nm
2
Multiples of SI Units (prefix)
9
giga
G
10
mega M
106
3
kilo
k
10
Other common symbols (English units)
psi = lbf / in2 ,
psf = lbf / ft 2
kip = 103 lbf
Newton (N)
Pascal (Pa)
Joule (J)
 2000, W. E. Haisler
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Review of General Principles (RS 1, 12)
Some Unit Conversions you should memorize!
Special SI definitions: Force: 1 N  1 kg m/s2
2
2
Pressure: 1 Pa  1 N/m = 1 kg/(m-s )
Length:
2.54 cm = 1 in
Mass: 1 slug = 14.59 kg, 1 lbm = 454 g (or 1 kg = 2.2 lbm )
Force: 1 lbf = 4.448 N (or 1 N = 0.225 lbf )
Pressure: 1 kPa = 0.145 psi (or 1 psi = 6.895 kPa)
Volume: 1 ft3 = 7.48 gal
1 qt = 0.946 l,
Standard Values:
1 l = 103 cm3
1 atm = 14.7 psi
Water weighs: 1 gm/cm3 (or 62.4 lbm/ft3)