AGENDA Unit 1 Measurement and Matter Test 1/24/12 Notes/handouts Elements Quiz #1-20 on Friday

Measurement Unit Metrics Scientific Notation Significant Figures Dimensional Analysis Density

Exact vs Measured Numbers Exact numbers are counts not measurements. Ex. A dozen= 12; a minute = 60 seconds Measured numbers have some uncertainty because of the measuring device.

Types of Measurement Qualitative measurement: uses words ex. A yellow-green gas was released. Quantitative measurement: uses numbers ex. The oxide has a mass of grams.

Metric Prefixes Powers of 10 Know the Metric Prefix to Power of 10 Tera (10 9 ) to femto ( ) Show chart and Practice Examples on board

Metric Prefixes

Precision vs. Accuracy PRECISION: Replication of results ex. A penny is massed 3 times g, 2.6g, 2.6g ACCURACY: True or correct results

Results can be precise, but not accurate. Ex. The penny massed 3 times at 2.6 g was precise, but placed on a faulty balance so the results are inaccurate. Bull’s Eye Example

Significant Figures (Digits) The accuracy of any measurement depends upon the instrument and the observer. The digits in an answer which imply more accuracy than the measurements justify are not significant and should be dropped so that those digits which remain represent the accuracy of the original measurement and are called SIGNIFICANT DIGITS

Computation Rules for Significant Digits 2 Main Rules Rule #1: Addition and Subtraction Rule: The answer cannot be anymore accurate than the least accurate DECIMAL place of the given Example: next slide

Rule # = (calculator answer) 88.6 (Rounded answer w/ rule)

Rule #2 Multiplication and Division The answer cannot be anymore accurate than the least NUMBER of significant digits of the given Example: /1.23 = (calculator answer) 3.09

Seven Base SI Units Length meter (m) Mass kilogram (kg) Time second (s)

Amount mole (mol) Electric current ampere (amp) Luminous intensity candela (cd)

Temperature Kelvin (K)

Quantity A quantity includes both a number and a standard unit Examples: 14.5 g 12 mi A quantitative measurement!!!!

Percent Error % Error = error/accepted value x 100 Error = experimental- accepted (+ difference)

DERIVED UNITS A combination of two or more units. Examples: Speed miles/hr ft/sec DENSITY is the mass per volume.