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cee4324-5984_lecture2

# cee4324-5984_lecture2 - CEE 4324/5984 Open Channel Flow...

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Glenn E. Moglen Department of Civil & Environmental Engineering Virginia Tech Significant Figures & Begin Specific Energy CEE 4324/5984 –Open Channel Flow – Lecture 2

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Call Roll Moglen’s Windmill: Significant Figures Specific Energy Definition Example 1: One energy, two depths Example 2: Minimum energy (critical depth) Example 3: Sluice Gate (conservation of E ) Example 4: Sluice Gate (concept of choke) Today’s Agenda
Rule 1: Exact numbers have infinite significant digits. Ex: A dozen eggs is exactly 12 eggs. Rule 2: Zeros used just to position the decimal point are not significant figures. Trailing zeros are not significant unless a decimal point is explicitly indicated. Ex: 0.0234 has 3 significant figures Ex: 2 0 has 1 significant figure Ex: 20 . has 2 significant figures Ex. 20.0 has 3 significant figures For Starters: Significant Figures

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Rule 3: In multiplication and division, an answer contains no more significant figures than the least number of significant figures used in the operation. Ex: For Starters: Significant Figures (cont.) result) (reported 15.2 result) r (calculato 1782 . 15 ) 23 . 1 ( ) 34 . 12 ( = = = = w L A
Rule 4: In addition and subtraction, the last digit retained in the sum or difference is determined by the first doubtful digit. Ex: For Starters: Significant Figures (cont.) result) (reported 6.64 result) r (calculato 6.6355 doubtful) is (5 21.2345 - doubtful) is (7 27.87 27.87 from 21.2342 Subtract

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Fact 1: Car generally gets between 40 and 50 mpg depending type of driving and season Fact 2: Fuel efficiency is reported on dashboard to the tenth’s place (e.g. 44.6 mpg) Observation: Although efficiency is reported to the tenths place, certain efficiency values are never seen. For instance, the progression of reported values between 44 and 45 mpg is: 44.2, 44.4, 44.6, 44.9 (you’ll never see 44.1, 44.3, 44.5, 44.7, 44.8) Explain? Significant Digits: Real World Example: Dr. Moglen’s Honda Civic Hybrid
Dr. Moglen’s theory: Fuel efficiency is actually calculated internally in units of km/liter and truncated to 1 decimal place (e.g 18.6 km/liter).

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