Transcript Set 1
CHAPTER 1 : MEASUREMENTS SIGNIFICANT FIGURES AND CALCULATIONS Significant figures and calculations Significant figures in a measurement include all of the digits that are known, plus one more digit that is estimated. Significant Figures •Any digit that is not zero is significant 2.234 kg 4 significant figures •Zeros between non-zero digits are significant. 607 m 3 significant figures • Leading zeros (to the left) are not significant. 0.07 L 1 significant figure. 0.00520 g 3 significant figures Trailing ( to the right) only count if there is a decimal in the number. 5.0 mg 2 significant figures. 50 mg 1 significant figure. Two special situations have an unlimited number off Significant figures: 1.. Counted items a) 23 people, or 425 thumbtacks 2 Exactly defined quantities b) 60 minutes = 1 hour Practice #1 How many significant figures in the following? 1.0070 m 5 sig figs 17.10 kg 100,890 L 3.29 x 103 s 0.0054 cm 3,200,000 mL 5 dogs 4 sig figs 5 sig figs 3 sig figs 2 sig figs 2 sig figs unlimited This is a counted value Rounding Calculated Answers Decide how many significant figures are needed Round to that many digits, counting from the left Is the next digit less than 5? Drop it. Next digit 5 or greater? Increase by 1 3.016 rounded to hundredths is 3.02 • 3.013 rounded to hundredths is 3.01 • 3.015 rounded to hundredths is 3.02 • 3.045 rounded to hundredths is 3.04 • 3.04501 rounded to hundredths is 3.05 Addition and Subtraction The answer should be rounded to the same number of decimal places as the least number of decimal places in the problem. Examples: 1 decimal places 4.8 3 decimal places -3.965 0.835 0.8 Make the following have 3 sig figs: M 761.50 14.334 10.44 10789 8024.50 203.514 762 14.3 10.4 10800 8020 204 Multiplication and Division Round the answer to the same number of significant figures as the least number of significant figures in the problem. Multiplication and Division: # sig figs in the result equals the number in the least precise measurement used in the calculation. 6.38 x 2.0 = 12.76 13 (2 sig figs) Addition and Subtraction: The number of decimal places in the result equals the number off decimal places in the least precise measurement. 6.8 + 11.934 =18.734 18.7 (3 sig figs) 89.332 + 1.1 = 90.432 round off to 90.4 one significant figure after decimal point 3.70 -2.9133 = 0.7867 two significant figures after decimal point round off to 0.79 Scientific Notation What is scientific Notation? Scientific notation is a way of expressing really big numbers or really small numbers. It is most often used in “scientific” calculations where the analysis must be very precise. Why use scientific notation? For very large and very small numbers, these numbers can expressed in a more concise form. Numbers can be used in a computation with far greater ease. Scientific notation consists of two parts: A number between 1 and 10 A power of 10 N x 10x Changing standard form to scientific notation. EXAMPLE 5 500 000 = 5.5 x 106 We moved the decimal 6 places to the left. A number between 1 and 10 EXAMPLE #2 0.0075 = 7.5 x 10-3 Numbers less than 1 will have a negative exponent. We moved the decimal 3 places to the right. A number between 1 and 10 EXAMPLE #3 CHANGE SCIENTIFIC NOTATION TO STANDARD FORM 2.35 x 108 = 2.35 x 100 000 000 = 235 000 000 Standard form Move the decimal 8 places to the right EXAMPLE #4 9 x 10-5 = 9 x 0.000 01 = 0.000 09 Standard form Move the decimal 5 places to the left TRY THESE Express in scientific notation 1) 421.96 2) 0.0421 3) 0.000 56 4) 467 000 000 TRY THESE Change to Standard Form 1) 4.21 x 105 2) 0.06 x 103 3) 5.73 x 10-4 4) 4.321 x 10-5 To change standard form to scientific notation… Place the decimal point so that there is one non-zero digit to the left of the decimal point. Count the number of decimal places the decimal point has “moved” from the original number. This will be the exponent on the 10. Continued… If the original number was less than 1, then the exponent is negative. If the original number was greater than 1, then the exponent is positive. Types of Errors Random errors- the same error does not repeat every time. • Blunders • Human Error Systematic Errors – These are errors caused by the way in which the experiment was conducted. In other words, they are caused by flaws in equipment or experimental. Can be discovered and corrected. Examples: You measure the mass of a ring three times using the same balance and get slightly different values: 12.74 g, 12.72 g, 12.75 g. ( random error ) The meter stick that is used for measuring, has a millimetre worn off of the end therefore when measuring an object all measurements are off. ( systematic error ) Accuracy or Precision • Precision Reproducibility of results Several measurements afford the same results Is a measure of exactness • Accuracy How close a result is to the “true” value Is a measure of rightness Accuracy vs Precision π 3 Accuracy Precision NO NO 7.18281828 NO YES 3.14 YES NO 3.1415926 YES YES Metric Conversions Ladder Method Ladder Method 1 2 3 KILO 1000 HECTO DEKA 100 Units 10 Units Units Meter s Liters Gram s How do you use the “ladder” method? 1st – Determine your starting point. 2nd – Count the “jumps” to your ending point. 3rd – Move the decimal the same number of jumps in the same direction. DECI 0.1 Unit CENTI 0.01 MILLI Unit 0.001 Unit 4 km = _________ m Starting Ending Point Point How many jumps does it take? 4. __ __ __ . 1 .2 . 3 = 4000 m Conversion Practice Try these conversions using the ladder method. 1000 mg = _______ g 1 L = _______ mL 14 km = _______ m 109 g = _______ kg 160 cm = _______ mm 250 m = _______ km Compare using <, >, or =. 56 cm 6m 7g 698 mg Metric Conversion Challenge Write the correct abbreviation for each metric unit. 1) Kilogram _____ 4) Milliliter _____ 7) Kilometer _____ 2) Meter _____ 5) Millimeter _____ 8) Centimeter _____ 3) Gram _____ 6) Liter _____ 9) Milligram _____ Try these conversions, using the ladder method. 10) 2000 mg = _______ g 15) 5 L = _______ mL 20) 16 cm = _______ mm 11) 104 km = _______ m 16) 198 g = _______ kg 21) 2500 m = _______ km 12) 480 cm = _____ m 17) 75 mL = _____ L 22) 65 g = _____ mg 13) 5.6 kg = _____ g 18) 50 cm = _____ m 23) 6.3 cm = _____ mm 14) 8 mm = _____ cm 19) 5.6 m = _____ cm 24) 120 mg = _____ g