ENG 243 - Statics
Introduction
Engineering Mechanics
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Describe how forces affect bodies
Applied Physics
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Equations of Motion
Equations of Equilibrium
Applied to real-world situations
Mechanics Courses
Statics
Rigid Bodies
No Acceleration
Dynamics
Strengths of Mat’ls
Rigid Bodies
Acceleration
Deformable Bodies
No Acceleration
Crane Example
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How does the crane cable affect the
object?
If the box moves first, what happens?
If the crane moves first, what happens?
What forces affect the crane boom?
Units
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4 units – 3 basic, 1 derived
 USC
SI
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Mass – kg
Length – m
Time – s
Force – derived
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F = m·a
W = m·g
1 kg·m/s2 = 1 N
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Force – lb
Length – ft
Time – s
Mass – derived
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m = F/a
m = W/g
1 lb/ft/s2 = 1 slug
Units
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Be careful with conversions
SI: g = 9.81 m/s2
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Determine the weight of a 15-kg block
USC: g = 32.2 ft/s2
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Determine the mass of a 200-lb block
Significant Digits
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Carry intermediate answers
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Round off last answer
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Carry at least one extra digit
Don’t round exact numbers – trig functions
If the answer begins with 1, show 4
For all others, show 3
Example: 1.237  0.243
Calculators
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Basic Scientific
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Sin, Cos, Tan
Square roots/Powers
Polar/Rectangular
Advanced Scientific
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Simultaneous Equations
Vectors – Cross Products
Problem Solving
1.
2.
3.
4.
5.
6.
7.
8.
Sketch
Given:
Find:
Primary relationship (equation)
Secondary relationships, assumptions
Rewrite to final form
Plug in numbers and units
Check that you’ve solved the problem
Example Problem
A concrete column has a diameter of 350 mm and a
length of 2 m. If the density of concrete is 2.45 Mg/m3,
determine the weight of the column, in pounds.
1. Sketch
2. Given:
2m
3. Find:
350 mm
Example Problem
A concrete column has a diameter of 350 mm and a
length of 2 m. If the density of concrete is 2.45 Mg/m3,
determine the weight of the column, in pounds.
4. Primary equation
5. Secondary equations
2m
6. Rewrite to solve
350 mm
Example Problem
A concrete column has a diameter of 350 mm and a
length of 2 m. If the density of concrete is 2.45 Mg/m3,
determine the weight of the column, in pounds.
7. Plug in numbers and units
2m
8. Check that you’ve solved the problem
350 mm