Measurement and Accuracy.pdf - Measurement and Accuracy Stephen Gosnell Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International

# Measurement and Accuracy.pdf - Measurement and Accuracy...

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Unformatted text preview: Measurement and Accuracy Stephen Gosnell Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License (unles otherwise noted) 1 Goals ▪ Describe the base of the metric system ▪ Relate measures based on pre-ﬁxes ▪ Be able to convert among units ▪ Be able to express numbers in scientiﬁc notation and convert to/from standard notation ▪ Be able to describe the diﬀerence between accuracy and precision and explain why each matters ▪ Use basic tools 2 Why Do We Measure Things? 3 Why Do We Measure Things? ▪ Trade! ▪ Taxes! ▪ Construction! Petrejus, Johann (Drucker), 1547, Waage 4 How Long? How Much? ▪ Measuring is common act ▪ Central to commerce and trade ▪ Has varied over time ▪ Roman mile ▪ Kings foot ▪ Always hierarchical (unit matches scale) ▪ Needs to be standardized (now globally) Petrejus, Johann (Drucker), 1547, Waage 5 Metric System ▪ Base 10 ▪ Standard preﬁxes attached to standard units ○ ○ ○ By Ian "Mister" Guch [CC BY-SA 4.0 ( )], from Wikimedia Commons gram (mass) meter (length) liter (volume) 6 Dimensional Analysis Aids In Converting Units Or Among Systems 7 Scientiﬁc Notation ▪ Scientists use some really big and really small numbers ▪ Notation lets us get rid of some of the digits ▪ 1,325,134,207 ~ 1.32 x 109 ▪ .0000006780797 ~ 6.78 x 10-7 ▪ Signiﬁcant ﬁgures Brian Brondel at English Wikibooks [GFDL ( ) or CC BY-SA 2.5 ( )], via Wikimedia Commons 8 Accuracy Vs Precision Is Key To Experiments ALL IMAGES HAVE 5 DOTS ON THEM! 9 This Really Matters ! By NASA/JPL/Corby Waste [Public domain], via Wikimedia Commons ▪ Mars Climate Orbiter crashed because two engineering groups designed thrusters and computers ▪ Impulse produced by thrusters given in imperial metrics, positioning software expected metric units 10 Tools ▪ Balance ▪ Tare By Stan Zurek [GFDL ( ), CC-BY-SA-3.0 ( s/by-sa/3.0/) or CC BY-SA 2.5 ( es/by-sa/2.5)], from Wikimedia Commons 11 Tools ▪ Balance ▪ Tare ▪ Pipette > Graduated Cylinder > Flask, Beaker (in regards to accuracy and precision, due to meniscus and pouring issues) ▪ Thermometer By Lucasbosch [CC BY-SA 3.0 ( es/by-sa/3.0)], from Wikimedia Commons 12 Pipettes ▪ Always point pipette down and match tip to correct pipette ▪ Measurements go from bottom of tip PRHaney [CC BY-SA 3.0 ( es/by-sa/3.0)] 13 Today ▪ In class ▪ Show me when you have sugar weighed out (Mass #8) ▪ Explain conversion of F to C for body temperature (Temperature #2) ▪ Have your group explain scientiﬁc notation to me 14 ...
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• Fall '13
• Mcclelland
• International System of Units, Wikipedia, Petrejus