1 Scientific Processes

2 The Scientific Method

observation exercise / hypothesis activity 3 Our Scientific Method  Make an observation  Consult authority  Make a prediction  Form a hypothesis  Test the hypothesis (experiment)  Analyze results  Accept/ reject hypothesis  Communicate results

Sponge Bob activity 4 Designing an Experiment  A good experiment seeks to prove a hypothesis false  Parts of an experiment: Test groupTest group Control groupControl group Independent variableIndependent variable Dependent variableDependent variable

5 Scientific Notation  A short-hand way to write really, really large or small numbers 3 x x 10 2  The whole number is the coefficient  The 10 is the base  The superscript is the exponent

6 Advantages to Using Scientific Notation  Saves space  Indicates the accuracy/precision of the number  Makes the number easier to manipulate in calculations

7 Rules of Calculation  Whole numbers have a positive exponent  Fractions have a negative exponent  When numbers are multiplied, the exponents are added  When numbers are divided, the exponents are subtracted

8 Practice Sci-Notation  Write the following in scientific notation:  Write the following in standard notation 4.23 x x x 10 5

9 Practice: Calculations  (2.0 x 10 2 ) x (4.3 x 10 5 )  6.3 x 10 1 ) x (5.0 x 10 6 )  3.6 x 10 6 / 2.0 x 10 5  4.8 x 10 9 / 2.2 x 10 6

10 Significant figures  Measurements are only as accurate & precise as the instrument producing the measurement  Significant figures are used to express the accuracy of a number

11 Sig-fig Rules  Numbers 1-9 are always significant  Zeros between significant figures are always significant  Trailing zeros are significant only if the number contains a decimal point  Zeros in the beginning of a number are not significant  Zeros following a decimal significant figure are significant

12 Examples  123 has three sig-figs  has four sig-figs  has four sig-figs but 3000 has only one sig-fig  has two sig-figs  has three sig-figs but has 5 sig-figs

13 Practice: Sig-figs  Determine the number of sig-figs in the following numbers:

14 Calculating with Sig-figs  In multiplication or division limit and round to the least number of significant figures in any of the factors  Ex: 23.0 cm x 432 cm x 19 cm = cm 3 the answer is expressed as cm 3 since 19 cm has only two sig-figs

15  In addition or subtraction, limit and round your answer to the least number of decimal places in any of the numbers that make up your answer  Ex: ml ml ml = ml  The answer is expressed as ml since 46.0 ml has only once decimal place

16 Percent Error  A way to express how far off a laboratory value is from the accepted value  Formula: % error = (accepted value - experimental value / accepted value) x 100

17 Practice: Percent Error  E.V. = 1.24 g A.V. = 1.30 g % error = 4.62 % error = 4.62  E.V. = 252 ml A.V. = 225 ml % error =  E.V. = 1.24 x A.V. = 9.98 x % error = x 10 -5

18 Measurements  Two systems: British & Metric  British is used in U.S.A. standard units: foot, pound, gallon standard units: foot, pound, gallon  Metric is used worldwide standard units: meter, kilogram, standard units: meter, kilogram, liter liter

19 British System  Long history of use; comfortable  Problems: awkward relationships between units which must be memorized; time consuming calculations

20 Metric System  Systeme Internationale  Base ten system  Prefixes are constant  Easily understood relationships between units; simple calculations

21 Conversion Factors  Conversion factors are composed of two numbers representing the same value ( i.e. 12 inches = 1 foot)  Conversion factors have a value of one  Conversion factor method allows us to shift from one unit to another ( i.e. inches to feet)

22 Conversion Factor Method  Involves cross multiplying the original unit and the conversion factor  Step one: write the given number & unit  Step two: set up a conversion factor - place the given unit as the denominator of the conversion factor - place desired unit as a numerator - place a “1” in front of the larger unit - determine the number of smaller units to make “1” of the larger units  Step three: cancel units. Solve the problem

23 Examples  Convert 2 miles to inches 2 miles x ft x 12 inches = in 1 mile 1 foot 1 mile 1 foot The answer is (in sig-figs)  How many seconds are in 4 days? 4 days x 24 hours x 60 min x 60 sec = sec 1 day 1 hour 1 min 1 day 1 hour 1 min The answer is sec (in sig-figs)

24 Practice: Conversion Factors  35 ml = ____ dl  950 g = ______ kg  2.5 yds = _____ in  18 pints = _____ pecks  5.5 kg = ______ lbs  27 miles = ______ km Express all answers in sig-figs