Thursday, October 31, 2013  Happy Halloween!  Standard IE1: Scientific progress is made by asking meaningful questions and conducting careful scientific experiments.  Independent Practice:  Section 3.3 Reading Packet  Question: Copy the chart into your Journal. QuantitySI Base Unit Symbol LengthMeterm MassKilogramkg TempKelvinK TimeSeconds Amount of Substance Molemol Luminous Intensity Candelacd Electric Current AmpereA

Measurements and Calculations

Units of Measurement  Measurements involve NUMBER and UNIT  Represent a quantity : has magnitude, size, or amount  Gram = unit of measurement  Mass = quantity

Units of Measurement  Scientists around the world agree on one system…  International System of Units (le Systeme International d ’ Unites)  SI units  Built from seven base units

SI Base Units

Units of Measurement

 Metric Prefixes – make units easier to use  Make the unit smaller or larger  Unit = prefix + base unit  Table pg. 74

Mass  Measures quantity of matter  SI unit: kilogram, kg  ______ kg = _____ g  gram used for smaller masses  Weight: measure of gravitational pull

Length  SI unit: meter, m  Longer distances: kilometer, km  _______ km = _______ m  Shorter distances: centimeter, cm  _______ m = ________ cm

Volume  SI unit: m 3  A derived unit: combination of base units by multiplying or dividing  SI unit for Area : l x w = m x m = m 2  Volume : l x w x h = m x m x m = m 3  Also: liters (L), mL, dm 3 and cm 3  1 L = 1 dm 3 = 1000mL = 1000 cm 3

Derived Units

Scientific Notation  Put the numbers in the form a x 10 n  a has one # to left of decimal  If # is bigger than 1  + exponent  If # is less than 1  - exponent

Scientific Notation  Review: Write in scientific notation or standard notation. a. 32,700 b c x d x 10 8

Let’s Practice Scientific Notation Worksheet

Significant Figures (Sig Figs)  How many numbers mean anything?  When we measure, we can (and do) always estimate between the smallest marks

Significant Figures (Sig Figs)  Better marks better estimate.  Last number measured actually an estimate 21345

Rules for Significant Figures 1) All nonzero digits are significant. 457 cm has 3 sig figs 2.5 g has 2 sig figs 2) Zeros between nonzero digits are significant kg has 4 sig figs g has 4 sig figs 3) Zeros to the left of the first nonzero digit are not significant. They are not actually measured, but are place holders g has 2 sig figs kg has 2 sig fig 4) Zeros at the end of a number and to the right of a decimal are significant. They are assumed to be measured numbers g has 4 sig figs 0.20 has 2 sig figs has 4 sig figs 5) When a number ends in zero but contains no decimal place, the zeros may or may not be significant. We use scientific (aka exponential) notation to specify kg may have 1, 2, 3 or 4 sig figs!

Sig Figs  What is the smallest mark on the ruler that measures cm?  142 cm?  140 cm?  Does the zero mean anything? (Is it significant?)  They needed a set of rules to decide which zeroes count.

Sig Figs.  g  4050 g  g  g  g

Sig Figs  Only measurements have sig figs.  Counted numbers are exact – infinite sig figs  A dozen is exactly 12  Conversion factors: 100 cm = 1 m

Problems  50 has only 1 significant figure  if it really has two, how can I write it?  Scientific notation  5.0 x sig figs  Scientific Notation shows ALL sig figs

Rounding Rules  Round to four sig figs  to three sig figs  to two sig figs  to one sig fig

Sig Figs  How many sig figs in the following measurements?  458 g  4085 g  4850 g  g  g  g

Let’s Practice Significant Figures Worksheet

Journal - Thursday, November 7, 2013  Standard IE1: Scientific progress is made by asking meaningful questions and conducting careful scientific experiments.  Independent Practice:  Significant Figures Worksheet (#2)  Question: Copy the chart into your Journal. (next slide)

PrefixMeaningFactor Mega (M)1 million times larger than unit 10 6 Kilo (k)1,000 times larger than unit 10 3 Deci (d)10 times smaller than unit Centi (c)100 times smaller than unit Milli (m)1,000 times smaller than unit Micro (μ)1 million times smaller than unit Nano (n)1,000 million times smaller than unit Pico (p)1 trillion times smaller than unit

OPEN NOTE Quiz!!  When?  Blocks 1 and 3: Wednesday, November 13, 2013  Blocks 2 and 4: Thursday, November 14, 2013  Topics Included:  SI Units  Scientific Notation  Significant Figures  Significant Figures in Calculations  Density  Conversions

Vocabulary Review  Calibration: a set of graduations to indicate values or positions.  Precision: Describes the closeness, or reproducibility, of a set of measurements taken under the same conditions.  Convey: To make something known to someone.  Significant: Very important.  Intervals: A period of time between events.

Review: Scientific Notation and Significant Figures Worksheets

Calculations with Significant Figures Rules Annotate the Reading

Calculations with Sig Figs g g g g 2. (35.6 L L) / = x ( m – 3.88 m) = Answers: 57g9.31 L31.62 m

Let’s Practice Significant Figures in Calculations WS

Density  Density = massD = m volume V  Units: g/cm 3 or g/mL but SI unit is kg/m 3  derived unit  Used to identify substances  Varies with temperature  As temp. increases density…

Density

Density Examples  If a metal block has a mass of 65.0 grams and a volume of 22 cubic centimeters, what is the density of the block?  D = m V  D = 65.0 g = 3.0 g/cm 3 22 cm 3

Density Examples  Aluminum has a density of 2.7 g/cm 3. What volume of aluminum has a mass of 60 grams?  D = M V 20 cm 3

Density Examples  Gold has a density of 19.3 g/cm 3. A block of metal has a mass of 80 g and a volume of 12 cm 3. Could this block be a piece of gold?  No, because this block has a density of 7 g/cm 3s

Journal – Friday, November 8, 2013  Standard:  IE1: Scientific progress is made by asking meaningful questions and conducting careful experiments.  Independent Practice:  Revise Section 3.3 Reading Packet  Calculate the Following (mind your sig figs):  ( ) x 12.4  ( ) / 9

Review – Sig Figs in Calculations

Unit Conversions

 Given information in one unit  need to find the equivalent in another unit 1. Identify what ’ s given 2. Organize plan of attack 3. Carry out plan WITH UNITS!!

Conversion factors  “ A ratio of equivalent measurements. ”  Start with two things that are the same. 1 m = 100 cm  Can divide by each side to come up with two ways of writing the number 1.

Conversion factors 100 cm1 m= 100 cm

Conversion factors 1 1 m= 100 cm

Conversion factors 1 1 m= 100 cm =1 m

Conversion factors 1 1 m= 100 cm = 1 m 1

Conversion Factors  Unique way of writing the number 1.  Does NOT change the VALUE, it changes the UNITS.

Write the conversion factors for the following  kilograms to grams  feet to inches  1 L = 1 dm 3 = 1000mL = 1000 cm 3

Method for Converting 1. T-Chart or Factor Label Method 2. Steps: Draw a Great Big “T” Put the number the problem gives you to convert to the top left of the “T” Put the unit of that number in the bottom right part of the “T” Write the units of what you want in the top right Write the unit conversion factor in front of the units from Steps 3 and 4.

Let ’ s Try Some!  323 mm = _____ nm  3.2 miles = _____ in  250 gallons = _____ mL  15 days = _______ min

More Unit Conversions More Involved

Derived Unit Conversions  54.3 cm 3 = ______ m 3  7.54 ft 2 = _______ in 2

Derived Unit Conversions  m/s = ______ mi/hr  625 g/mL = ______ kg/m 3  100 km/hr = ______ mi/hr

Let’s Practice Dimensional Analysis

Where do these measurements come from? Recording Measurements

Making Good Measurements  We can do 2 things: 1. Repeat measurement many times - reliable measurements get the same number over and over - this is PRECISE

Making Good Measurements 2. Test our measurement against a “ standard ”, or accepted value - measurement close to accepted value is ACCURATE

Measurements are Uncertain 1. Measuring instruments are never perfect 2. Skill of measurer 3. Measuring conditions 4. Measuring always involves estimation  Flickering # on balance  Between marks on instrument

Estimating Measurements

Error  Probably not EXACTLY 6.35 cm  Within.01 cm of actual value.  6.35 cm ±.01 cm  6.34 cm to 6.36 cm

Calculating Percent Error  Compares your measurement to accepted value  Negative if measurement is small  Positive if measurement is big

Calculating Percent Error  What is the % error for a mass measurement of 17.7g, given that the correct value is 21.2g?

Let’s Practice Percent Error Worksheet