Transcript Section 1.1-1.6 Lecture Slides

Professor David Martinez
Introductions
Course Syllabus
 Student introductions:

 Name, Major, Hometown, Favorite Subject in
HS, Why do you think engineers need to
know statics?
WHAT IS MECHANICS?
• Study of what happens to a “thing” (the technical name is
“BODY”) when FORCES are applied to it.
• Either the body or the forces could be large or small.
BRANCHES OF MECHANICS
Mechanics
Rigid Bodies
(Things that do not change shape)
Statics
Dynamics
Deformable Bodies
(Things that do change shape)
Fluids
Incompressible
Compressible
Statics: equilibrium of bodies, bodies at rest or moving with
constant velocity
Dynamics: concerned with accelerated motion of bodies
WHAT MAY HAPPEN IF STATICS IS NOT
APPLIED PROPERLY?
Summer 2008: Engineering Lowlight
The Great Sichaun Earthquake (May 12, 2008)
 Magnitude 8.0 earthquake left more than 50,000 people dead

Great Sichaun Earthquake

What is an 8.0 earthquake?
 Richter Scale magnitude 8.0 earthquake is equivalent to 33 times
the force of the atomic bomb dropped over Nagasaki during WWII

How many people is 50,000?
 Los Angeles Coliseum holds 92,516 people
 Imagine going to a USC football game and just under half the
people in attendance are allowed to go home. I think I’ll watch the
game at home!!

Would the same thing happen if Los Angeles experienced an
8.0 earthquake?
 Probably not, since the Chinese earthquake occurred in rural
China where buildings and structures were not built to withstand
such an earthquake (and possibly built without earthquakes in
mind!)
 Buildings and infrastructure in the Los Angeles area have to meet
strict building codes or the builders face serious fines and
penalties. There will more than likely be less damage if an 8.0
earthquake hit the Los Angeles region.
Summer 2007: Engineering Highlights
(…and lowlights)

Space Shuttle Endeavour lifted off Cape
Canaveral, FL on Aug. 8, 2007 to continue
space station construction by delivering a
third starboard truss segment.
Summer 2007: Engineering Highlights
(…and lowlights)

During take-off, foam loss from the liquid
oxygen feedline brackets on the external
tank during launch caused thermal tile
damage to Endeavour.
Summer 2007: Engineering Highlights
(…and lowlights)
Space shuttle
Endeavour is safe to
fly home as is
 Space Shuttle
Endeavour glided to a
perfect landing at
NASA's Kennedy
Space Center in
Florida on August 21.

Summer 2007: Engineering Lowlights

The I-35 bridge in Minneapolis, Minnesota
collapses. Official death toll is 13 with over
100 injured.
Summer 2007: Engineering Lowlights

U.S. highway bridges are, on average, 40 years old. The
typical interstate bridge was built in the late 1960s (the I35 bridge was finished in 1967).

Most bridges are inspected and rated every two years.

In 2005, engineers rated the I-35 bridge in Minnesota as
"structurally deficient" and possibly in need of
replacement.

Overall, about 20 percent of interstate bridges (nearly
12,000 bridges) were rated as deficient in one way or
another in 2004.
MECHANICS, UNITS, NUMERICAL CALCULATIONS & GENERAL
PROCEDURE FOR ANALYSIS (Sections 1.1-1.6)
Today’s Objectives:
Students will be able to:
a) Identify what is mechanics / statics.
b) Work with two types of units.
In-Class activities:
c) Round the final answer appropriately. • Concept Review
d) Apply problem solving strategies.
• What is Mechanics
• System of Units
• Numerical Calculations
• Concept Challenge
• Problem Solving Strategy
• Attention Review
Concept Review
1. The subject of mechanics deals with what happens to a body
when ______ is / are applied to it.
A) magnetic field
B) heat
D) neutrons
E) lasers
C) forces
2. ________________ still remains the basis of most of today’s
engineering sciences.
A) Newtonian Mechanics
B) Relativistic Mechanics
C) Greek Mechanics
C) Euclidean Mechanics
UNITS OF MEASUREMENT
(Section 1.3)
• Four fundamental physical quantities.
•Length
•Mass.
•Time
•Force:
• Newton’s 2nd Law relates them: F = m * a
• We use this equation to develop systems of units.
• Units are arbitrary names we give to the physical quantities.
IDEALIZATIONS

Particle: geometry of object not involved, size of
object neglected.

Rigid Body: large number of particles remain at
fixed distances away from each other before and
after application of load.

Concentrated Forces: load acts on a single
point on a body.
Newton’s Laws of Motion

First Law: A particle originally at rest, or
moving in a straight line with constant
velocity, will remain in this state provided
the particle in not subjected to an
unbalanced force
Newton’s Laws of Motion

Second Law: A particle acted upon by an
unbalanced force F experiences an
acceleration a that has the same direction
as the force and a magnitude that is
directly proportional to the force. If F is
applied to a particle of mass m, this law
may be expressed mathematically as
F = ma
W = mg
Newton’s Laws of Motion

Third Law: The mutual forces of action
and reaction between two particles are
equal, opposite, and collinear.
UNIT SYSTEMS
• Force, mass and acceleration are called the base units.
• The fourth unit, time is derived from the acceleration term.
• We will work with two unit systems in statics:
•International System (SI)
•U.S. Customary (USCS)
Table 1-1 in the textbook summarizes these unit systems.
Reading Assignment for Thursday
Sections 2-1 to 2-4 (pgs. 17-37)
 HW assigned on Thursday
 Quizzes will start next Thursday
