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iii. Measurement

iii. Measurement. Units of Measurement SI Base Units & Prefixes Derived Units Calculations Significant Figures Precision and Accuracy. Metric System. Base Units Mass - kilogram (kg) Length- meter (m) Time - second (s) Temperature- Kelvin (K) Electric current- ampere (amp, A)

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iii. Measurement

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  1. iii. Measurement Units of Measurement SI Base Units & Prefixes Derived Units Calculations Significant Figures Precision and Accuracy

  2. Metric System • Base Units • Mass - kilogram (kg) • Length- meter (m) • Time - second (s) • Temperature- Kelvin (K) • Electric current- ampere (amp, A) • Amount of substance- mole (mol)

  3. Metric Conversions k h da UNIT d c m • 6000 liters = ________ kl • 0.23 g = _________mg • 5 hm= ________ cm • 9 g = ______ dg

  4. Density • Density – an object’s mass per unit volume • A physical property • Formula: • D = M / V • M – mass (g) • V – volume (mL) or (cm3)

  5. M D = D V C. Derived Units • Combination of base units. • Volume - length  _____  _______ 1 cm3 = 1 ____ • Density - mass per unit ______ (g/cm3)

  6. Your turn to try! • The density of an object is 2.6 g/ml. It has a mass of 9 grams. Give its volume. • A cube is 3 cm long, 3 cm wide, and 3 cm tall. It has a mass of 7 grams. What is its density? • The density of an object is 0.98 g/ml. It has a volume of 19 cubic cm. What is its mass?

  7. Significant Figures • Learn these rules: • All nonzero digits are significant. 876 • Zeros to right of decimal and to right of non zero digit are significant. 692.00 • Zeros between 2 nonzero digits are significant. 90,909 90,087.00101 • Zeros to the left of a decimal and left of a nonzero digit are not significant. 0.0210 • Zeros to the right of a decimal that serve as placeholders before nonzero digits are not significant. 0.0000003109901 • Zeros to the left of an understood decimal and to the right of nonzero digits are not significant. 9,340,010,000

  8. How many SF are in each? • 3,000.21 • 45.9009 • 9,090,000 • 821.000340 • 124,678 • 0.001201340 • 99.100 • 0. 90101

  9. Doing the math • Multiplication and division, same number of sig figs in answer as the least in the problem • Addition and subtraction, same number of decimal places in answer as least in problem.

  10. Operations Using SFs • Adding & Subtracting: Ex. 500.1 + 11.22 = 511.32 = 511.3 1 DP 2 DP 2DP 1DP Ex. 455.564 - 50.1 = 405.464 = 405.5 3DP 1DP 3DP 1DP

  11. Operations Using SFs • Multiplying and dividing: Ex. 500 x 11 = 5,500 = 6000 1 SF 2 SF 2SF 1SF Ex. 45/9.0 = 5 = 5.0 both have 2 SFs

  12. Try these • Answer the following in proper number of SFs. • 34.2 x 13 = • 9 x 2 = • 95.0/9 = • 1/4 = • 32/4.0=

  13. Uncertainty • Basis for significant figures • All measurements are uncertain to some degree • Precision- how repeatable • Accuracy- how correct - closeness to true value. • Random error - equal chance of being high or low- addressed by averaging measurements - expected

  14. Uncertainty • Better precision implies better accuracy • You CAN have precision without accuracy • You CANNOT have accuracy without precision

  15. Accuracy and Precision Ex. You throw 3 darts. All three hit in the outer edge of the board within a few cm of each other. You are _______ with the throw but not ________. Ex. You throw 3 darts. All 3 hit in the center of the bulls eye. You throws were very _________ and they also were _________.

  16. Another example • You use a balance to get the mass of an object. You do it three times. You get the answers 8 g, 9 g, and 10 grams. Your average is 8 grams. The book value is also 7 grams. • Were you precise? • Were you accurate?

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