 # Unit 1 Chapter 2. Common SI Units SI System is set-up so it is easy to move from one unit to another.

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Unit 1 Chapter 2

Common SI Units

SI System is set-up so it is easy to move from one unit to another.

Units that arise from other SI units are called derived units.

Volume Volume is the amount of space occupied by an object. The derived SI unit is cubic meters, m 3 The cubic centimeter, cm 3, is often used The liter, L, is a non-SI unit 1 L = 1000 cm 3 1 mL = 1 cm 3

Volume

Conversion Factors A ratio derived from the equality between two different units that can be used to convert from one unit to another.

Conversion Factors

Precision and Accuracy Accuracy refers to the agreement of a particular value with the true value. Precision refers to the degree of agreement among several elements of the same quantity.

The Difference between Precision and Accuracy

Precision and Accuracy

Rules for Counting Significant Figures Nonzero integers always count as significant figures. 3456 4 sig figs Significant Figures Consist of all digits that are known with certainty plus one final digit which is uncertain or estimated.

Rules for Counting Significant Figures - Zeros Leading zeros do not count as significant figures. 0.0486 3 sig figs.

Captive zeros always count as significant figures. 16.07 4 sig figs Rules for Counting Significant Figures - Zeros

Trailing zeros are significant only if the number contains a decimal point. 9.300 4 sig figs Rules for Counting Significant Figures - Zeros

Rules for Significant Figures in Mathematical Operations Multiplication and Division: # sig figs in the result has the same number of significant figures as the number with the fewest significant figures. 6.38  2.0 = 12.76 Rounds to  13 (2 sig figs)

Rules for Significant Figures in Mathematical Operations Addition and Subtraction: the result has the same number of decimal places as the least precise measurement. 6.8 + 15.6896 = 22.4896 Rounds to  22.5 (3 sig figs)

is calculated by subtracting the accepted value from the experimental value, dividing the difference by the accepted value, and then multiplying by 100. Percent Error

Direct Proportions Two quantities are in direct proportion if dividing one by the other gives a constant value. Indirect Proportions Two quantities are inversely proportional if their product is constant.

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