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Conversions.

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Presentation on theme: "Conversions."— Presentation transcript:

1 Conversions

2 34m = _________ km

3 46 inches = __________ Feet

4 3.4 MJ = ________ J

5 2.9x107nl = _______ GL

6 Significant Digits

7 Measurements Every measurement is wrong! Examples: To a certain degree
Your Birthday Height

8 Every measurement has a degree of uncertainty
The uncertainty is based on: The measuring device The skill of the measurer

9 Ways to indicate How Accurate a Number Is
Tolerance Intervals Percent Error Significant Digits

10 Tolerance Intervals Tolerance is the greatest range of variation that can be allowed 25  0.5 would be between to 25.49 25  0.05 would be between to 25  would be between to

11 Tolerance Intervals Used on blueprints and in machining to indicate accuracy

12

13 Activity: Tolerance a Part
Design a square piece with a square hole through it’s centre. Key Dimensions: How must the length of the piece be toleranced How big must the square hole through the piece be to accommodate the square peg Criteria: The square piece must sit inside a container that was toleranced 20m  lm on each side The square peg is dimensioned 2m 0.1m

14 Percent Error Indicates a percentage that the value may be out by

15 Sample Problem You buy an 8 foot 2x4. You measure the board to be 94.5 inches long. What is the percentage error for the length of the board? 12 inches = 1 foot

16 Significant Digits The accuracy is determined by the right most digit
25 would be between to 25.49 25.0 would be between to 25.00 would be between to

17 Significant Digits: Uses the number of digits in the number to express the uncertainty of the number
1 x 101 is less accurate than 12 12 is less accurate than 12.0 12.0 is less accurate than 12.00

18 Rules for Significant Digits
All non-zero digits are significant All zeros contained between non-zero digits are significant i.e. 207 – 3sd All trailing zeros to the right of a decimal are significant i.e – 4sd

19 When are zeroes not significant?
All leading zeros to the left of the first non-zero digit are not significant i.e – 2 sd

20 Exact numbers have infinite significant digits
How many cars do I have? 1

21 Examples a.) 125.9 b.) 230 c.) d.) 500.3

22 Examples: a.) s.d. b.) s.d. c.) s.d. d.) s.d.

23 How to Improve Accuracy
Improve the measuring instrument The smaller the unit on the measuring device, the more precise the measurement Know how to measure Always look straight down on the measuring device Repeat Measure several times to get a good average value “Measure twice, cut once” Measure under controlled conditions Objects can shrink or expand based on measuring conditions

24 Why wouldn’t you make everything very, very accurate?
Cost Waste of time Not needed The more accurate a measurement must be, the more it costs to do so

25 Bibliography Britton. "Geometric Dimensioning and Tolerancing." Lecture. nicaldesign101/GDandT.pdf. 1 Feb. 2013


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