Davis. 1.Measurements 2.Understand Uncertainty in Measurement 3.Know, understand, and be able to apply significant figures to calculations. 4.Know,

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Presentation transcript:

Davis

1.Measurements 2.Understand Uncertainty in Measurement 3.Know, understand, and be able to apply significant figures to calculations. 4.Know, understand, and be able to apply scientific notation to calculations.

Defined: determination of the quantities related to an object. Dimensions Volumes Time Etc… Requires that someone actually

Two terms: 1.Exact numbers – Exactly Exactly _____ desks in this room. 1.Inexact numbers – Flaws in Uncalibrated User

Defined Precision –

Accuracy – Volume measurements for a titration: Trial 1 = 25.5 mL Trial 2 = 25.6 mL Trial 3 = 25.5 mL

Mass readings for a magnesium sample: Trial 1Trial 2Trial g0.157 g0.135 g Evaluate these measurements for precision and accuracy

Two teams of three students count birds sitting on a power line. Team counts are: Team ATeam B Marjorie: 71Howard: 76 Marlene: 74Alice: 76 Kathleen: 71Sharon: 67 Who was most accurate? Which team was most accurate? Which team’s count was most precise? The actual count was 76 birds.

Why are digits in measurements uncertain? 1.Instruments Differences 2.Always involves estimation  Choose the right instrument for the job  Volumetric vs ‘to hold’ glassware  May be estimated for you (electronic scales)  Scale is marked but you estimate the in- between

MUST Which is correct?

Method to deal with All digits known

All KNOWN numbers

The Rules – Memorize these. All non-zeros are A zero is significant when : It is A zero is not significant when: It is It is at

How many significant digits? ,000, ,000,000.1

Add/subtract – Multiply/divide – Only round after problem is complete

Addition and Subtraction Round answer to have final digit in the SAME PLACE as the last digit in the LEAST ACCURATE MEASUREMENT = = = = = =

Multiplication and Division The answer has as many sig figs as the number with the fewest sig figs 14.8 x 3.1 = 18.2 x 3.0 = 52/1.5 = x 1 = 2400 x = 15000/ =

x 78.5 =

/ =

Exact numbers are never used to determine the number of significant figures to report in your answer ft *1 mile 5280 ft = mile

Convenient way of writing very large or very small numbers and showing only significant figures Number between 5120 becomes Move decimal point in original number to make number 1-10 Move left = Move right =

123,000 = = = = 1,000,000 =

Express the number 275,364,145 with: 4 sig fig: 2 sig fig: 6 sig fig:

Math with: Use the EE or EXP button on your calculator. For example: