iii. Measurement I. Units of Measurement I.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)  Amount of substance- mole (mol)

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

Density  Density – an object’s mass per unit volume  A physical property  Formula:  D = M / V  M – mass (g)  V – volume (mL) or (cm 3 )

C. Derived Units  Combination of base units.  Volume - length  _____  _______ 1 cm 3 = 1 ____  Density - mass per unit ______ (g/cm 3 ) D = D M V

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?

Significant Figures  Learn these rules: 1. All nonzero digits are significant Zeros to right of decimal and to right of non zero digit are significant Zeros between 2 nonzero digits are significant. 90,909 90, Zeros to the left of a decimal and left of a nonzero digit are not significant Zeros to the right of a decimal that serve as placeholders before nonzero digits are not significant Zeros to the left of an understood decimal and to the right of nonzero digits are not significant. 9,340,010,000

How many SF are in each? 1. 3, ,090, ,

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.

Operations Using SFs  Adding & Subtracting: Ex = = DP 2 DP 2DP 1DP Ex = = DP 1DP 3DP 1DP

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

Try these  Answer the following in proper number of SFs x 13 = 2. 9 x 2 = /9 = 4. 1/4 = 5. 32/4.0=

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

Uncertainty  Better precision implies better accuracy  You CAN have precision without accuracy  You CANNOT have accuracy without precision

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 _________.

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?