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# sect1 - ABE 201 Biological Thermodynamics 1 Unit...

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1 ABE 201 Biological Thermodynamics 1 Section 1 Unit Conversion, Dimensions, Precision, and Accuracy Today’s Topics • Dimensions – A property that can be measured (mass, time, etc.) • Unit Conversion – How do you convert between lb and kg? – How do you convert between C and F? • Precision vs Accuracy – Can we trust our measurements of a system? Dimensions versus Units • Dimension is a property that can be measured • Dimensions have 2 parts: value and unit – Value is a number: 3.57 – Unit describes the number: kg, sec., C • Numerical values can only be added, subtracted, multiplied, or divided if they have the same units

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2 Unit Conversion • Convert each unit separately! – Some units are compound (force) and must be broken into constituent units • N to lbf – Some conversion tables have conversions for common compound units Unit Conversion • Watch your dimensions! – All dimensions should be converted – Don’t multiply same units together! – Convert 2.44 kJ/min to BTU/sec -4 kJ 1000 J 9.486 10 BTU 60 sec 2.44 * * * min 1 kJ 1 J 1 min -4 kJ 1000 J 9.486 10 BTU 1 min 2.44 * * * min 1 kJ 1 J 60 sec Parts per million or billion • A method of expressing the concentration of extremely dilute mixtures. • Solids and liquids: mass fraction • Gases: mole fractions • Example: What percent is 15ppm? 15 x 10 -6 x 100 = 15 x 10 -4 % or 0.0015% This is a pretty small percentage! Significant Figures • Significant figures: 100, 100.3, 100.300 1.47*3.0926 = 4.54612 correct? • 147 + 23.5 = 170.5 correct?
3 Measures of Central Tendency • Mean (aka arithmetic average) = average(a1:a20) • Median (50 th percentile) = median(a1:a20) • Mode (highest frequency) n x Σ μ = Measures of Spread • Variance =varp(a1:a20) • Standard Deviation =stdevp(a1:a20) ( 29 n - x Σ 2 2 μ σ = ( 29 n - x Σ 2 = Populations vs Samples • Important distinction • Population = all observations of a type • Sample = a subset of a population • Statistics allows predictions about parameters (e.g. mean) and statistics (e.g. standard deviation) of populations to be made based on a sample Population or Sample • Election count • Polling data • Class Survey (Homework 0) • Quality Control Test on Products • Final Grade

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4 Predicting Parameters and Statistics from Samples • Mean (aka arithmetic average) = average(a1:a20) • Standard Deviation = stdev(a1:a20) μ = n x Σ x ( 29 σ = 1 - n x - x Σ s 2 Accuracy vs Precision • Accuracy: How close is a measured value to the true value? • Precision: How much error is there in the measured value(s)? Accuracy • Do your measurements match the “true” value or are they skewed? • The
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## This note was uploaded on 12/09/2011 for the course ABE 201 taught by Professor Nathanmosier during the Fall '11 term at Purdue.

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sect1 - ABE 201 Biological Thermodynamics 1 Unit...

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