engr 152: statics lecture #1

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?

• Either the body or the forces could be large or small.

• Study of what happens to a “thing” (the technical name is “BODY”) when FORCES are applied to it.

BRANCHES OF MECHANICS

S ta tic s D yn am ics

R ig id B od ies(Th in g s th a t d o n o t ch an g e sh ap e)

D efo rm ab le B od ies(Th in g s th a t d o ch an g e sh ap e)

In com p ress ib le C om p ress ib le

F lu id s

M ech an ics

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 I-35 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.

c) Round the final answer appropriately.

d) Apply problem solving strategies.

In-Class activities:

• Concept Review

• 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 C) forces

D) neutrons E) lasers

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 = maW = 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