Transcript Section 1.1-1.6 Lecture Slides

ENGR 34
STATICS
Vince Bertsch
Office: Rm 1776
527-4621
[email protected]
Today’s Objectives
a) Define mechanics & statics
b) Overview of the course logistics and resources
c) Review units and vectors
d) Recap Newton’s Laws
WHAT IS MECHANICS??
•The study of what happens to a “thing”
when it gets “pushed”
WHAT IS STATICS??
•The study of what happens to a “thing”
when it gets “pushed” but doesn’t accelerate
BRANCHES OF MECHANICS
Mechanics
(study of push on things)
Rigid Bodies
(don't change shape)
Statics
(no change in motion)
Deformable Bodies
(do change shape)
Dynamics
(acceleration)
Incompressible
(hydrodynamics)
Fluids
Compressible
(aerodynamics)
Why do we care about statics?
Why do we care about statics?
COURSE GOALS
• Foundational knowledge of statics
• Analytical problem solving skills
• Calculator and computer skills
• Working together
• Free body diagrams
• # of equations, # of unknowns
COURSE MATERIALS
• Hibbeler, Engr. Mechanics Statics, 12th Ed
• Course workbook
• Mastering Engineering
MasteringEngineering.com
Engr 34
Statics
Workbook
• My homepage
online.santarosa.edu/homepage/vbertsch
• Course website
online.santarosa.edu/section/?5358
ESTIMATING UNIT CONVERSIONS
•1 m ≈ 3 ft
•1 km ≈ 0.6 mi
•25 mm ≈ 1 in
•1 kg ≈ 2 lb
•10 N ≈ 1 kg
Just multiply or divide by 10 or 2.
•1000N ≈ 1 vb
ESTIMATING PRACTICE
Estimating Practice
No calculators
Fill in the table with estimated values in the other units.
pounds
kilograms
newtons
143
3241
22
VECTOR REVIEW
Vectors have both a magnitude and a direction.
Vector variable names: AB or F
AB or F
^ ^^
^ ^ ^
^ z,
^ AB,
Unit vectors: i, j, k, ^x, y,
F, l
i,j,k, e
Force values:
F = 10#<100° (uses default defn for angle)
F = 40 N 80°
(uses picture to define angle)
F = 10 lb T (uses default object tension defn)
F = 15N (magnitude only, use arrow in diagram
for both direction and +/- significance)
2D COORDINATE CONVERSION
Approach #1 (manual):
Keep angles between 0 and 90,
sin for opposite, cos for adjacent,
do signs yourself.
Approach #2 (automatic):
Use standard defined angles,
(from x axis counter-clockwise),
input into calculator.
2D COORDINATE PRACTICE
2D Coordinate Conversions
Write the trigonometric relationships, do not solve.
Y
Y
Y
A
5
C
30°
X
X
9
B
7
50°
40°
Ax =
5cos(30°)
Bx =
-9sin(40°)
Ay =
5sin(30°)
By =
-9cos(40°) or 9sin(-130°)
or
9cos(-130°)
C =
7/sin(40°)
NEWTON’S LAWS
I
SF=0 iff no change in motion
II
F = ma
III
Equal & Opposite
BRING CALCULATOR TO CLASS