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EGR-140 Engineering Mechanics, Statics

EGR-140 Engineering Mechanics, Statics. Course Instructor Information : Paul Gordy, Engineering Program Head Tidewater Community College Pgordy@tcc.edu Office: H115 (Advanced Technology Center, VB Campus Room 1117 (Tri-Cities Center). Today’s Objectives : Students will be able to:

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EGR-140 Engineering Mechanics, Statics

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  1. EGR-140 Engineering Mechanics, Statics Course Instructor Information: Paul Gordy, Engineering Program Head Tidewater Community College Pgordy@tcc.edu Office: H115 (Advanced Technology Center, VB Campus Room 1117 (Tri-Cities Center)

  2. Today’s Objectives: Students will be able to: a) Explain mechanics / statics. b) Work with two types of units. c) Round the final answer appropriately. d) Apply problem-solving strategies. MECHANICS, UNITS, NUMERICAL CALCULATIONS & GENERAL PROCEDURE FOR ANALYSIS

  3. Either the body or the forcescan be large or small. WHAT IS MECHANICS? • Study of what happens to a “thing” (the technical name is “BODY”) when FORCES are applied to it.

  4. BRANCHES OF MECHANICS

  5. UNITS OF MEASUREMENT (Section 1.3) • Four fundamental physical quantities (or dimensions). • Length • Mass • Time • Force • Newton’s 2nd Law relates them: F = m * a • Units are arbitrary names we give to the physical quantities.

  6. We will work with two unit systems in statics: • International System (SI) • U.S. Customary (USCS) UNIT SYSTEMS • Force, mass, time and acceleration are related by Newton’s 2nd law.Three of these are assigned units (called base units) and the fourth unit is derived. Which is derived varies by the system of units.

  7. Table 1-1 in the textbook summarizes these unit systems.

  8. Weight Newton’s 2nd Law of Physics, F = ma can be used to calculate force for any acceleration. If a = g = acceleration due to gravity, then the force is referred to as weight and F = ma can be written as: W = mg Values for g Use the following values in this course for g = acceleration due to gravity: g = 32.2 ft/s2 (US units) or g = 9.81 m/s2 (SI units)

  9. Work with weight, not mass In this course we are generally concerned with working with forces. As a result, if the mass of an object is specified, you should convert the mass to a weight (force). Example: Determine the tension in each rope. (We will see how to solve this problem later, but as a first step we would typically convert the mass to a weight. Find the weight.) 30o 30o 45o 45o 2.2 slugs

  10. Example: Determine the tension in each rope. (We will see how to solve this problem later, but as a first step we would typically convert the mass to a weight. Find the weight.) 30o 30o 45o 45o 250 N Recall that the base unit for mass in the SI system is the kg, not the g)

  11. Work problems in the units given unless otherwiseinstructed! COMMON CONVERSION FACTORS • Example: Convert a torque value of 47 in • lb into SI units. • Use dimension analysis to convert by hand. • Also try it on a calculator. • Answer is 5.31026116 N • m?

  12. SI Prefixes

  13. THE INTERNATIONAL SYSTEM OF UNITS (Section 1.4) • No plurals • Example: m = 5 kg, not kgs • Example: W = 10.5 lb, not 10.5 lbs ) • Separate multiplied units with a • (e.g., meter second = m • s ) • Exponential powers apply to units, e.g., cm • cm = cm2 • Compound prefixes should not be used. • Scientific notation is not generally used with prefixes.

  14. NUMERICAL CALCULATIONS (Section 1.5) • Must have dimensional “homogeneity.” Dimensions have to be the same on both sides of the equal sign, (e.g. distance = speed  time.) • Use an appropriate number of significant figures (3 for • answer, at least 4 for intermediate calculations). Why? • Be consistent when rounding off. • - greater than 5, round up (3528  3530) • - smaller than 5, round down (0.03521  0.0352) • - equal to 5, see your textbook for an explanation.

  15. PROBLEM SOLVING STRATEGY: A Three Step Approach (IPE) 1. Interpret:Read carefully and determine what is given and what is to be found/ delivered. Ask, if not clear. If necessary, make assumptions and indicate them. 2. Plan: Think about major steps (or a road map) that you will take to solve a given problem. Think of alternative/creative solutions and choose the best one. 3. Execute: Carry out your steps. Use appropriate diagrams and equations. Estimate your answers. Avoid simple calculation mistakes. Reflect on / revise your work.

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