Unit 1: Measurement Flashcards
Measurement
assignment of numbers to an object or event
quantifies
Three arbitrary systems of measurement
- English (imperial)
- Metric
- SI
Exact Numbers
Count, definition, integer number
- No uncertainty
- 60 min/hour
- 1000 mL/ L
Inexact Numbers
- Measurement
- Uncertainty from estimation
- Tool precision limited
- Also limit to # decimal points
What is Precision?
how closely repeated measurements of the same quantity agree with one another
What is Accuracy?
how closely a measured value agrees with the correct value
Accuracy vs precision
2 kinds of Error
Random Error
Systematic Error
What is Random Error?
Skews data from multiple measurements in a more or less uniform way around some average value.
- Apparatus fluctuation,
- experiment flaw
- human error
What is Systematic Error?
causes data to be either larger or smaller than the accepted value. Can often be found and removed
- Inaccurate calibration,
- dust on balance pan,
- impurities in chemicals.
Significant Figures
digits that indicate the precision of measurements
digits of a measured number that have uncertainty only in the last digit.
Sig figs – “correct” to first estimated digit
Sig figs shows degree of uncertainty – precision
Must report proper significance
rules for sigfigs
- All nonzero numbers
- ex: 21.389, 2.1389 (5)
- Any zeros between nonzero numbers.
- ex: 80.005002 (8)
- Trailing zero’s (at the end of a number) if the number has a decimal place:
- ex: 67.700 (5), 10,000 (1), 12,100. (5)
- Leading zero’s insignificant (place holders)
- ex: 0.00009802 (4)
- Exact numbers are infinite
How many significant figures are in each of the following?
- 7.26
- 7.002
- 7.0
- 240
- 0.0720
How many significant zero’s in each of the following?
- 7.0063
- 0.0001399012
- 001000
- 100.000
- 0100.
Sig Figs in Addition and Subtraction
- Addition/Subtraction: # of sig figs is based on fewest decimals
- 37.68 + 108.428 + 6.71862
Sig Figs in Multiplication and Division
Multiplication/Division – based on fewest sig figs
4.237 x 1.21x10-3 x 0.00273 ÷ 11.125
Sig figs in exponents and logs
- Exponents like mult:
- (8.134x102)3
- (8.134x102)½
- Logs/antilogs: # decimals = sig figs in original #
- log 4.0x105
Report the following with the proper number of significant digits:
- 4.26 + 3.831
- 8.321 – 2.4
- 63.8 x 0.80
- 27.2 x 15.63 ÷ 1.84
