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, m3

The cubic centimeter, cm3, is often used

The liter, L, is a non-SI unit

1 L = 1000 cm3

1 mL = 1 cm3

Volume

Conversion FactorsA 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 experimentalvalue, dividing the difference by the accepted value, and then multiplying by 100.

experimental accepted

accepted

Value -ValuePercentage error = × 100

Value

Percent Error

Direct ProportionsTwo quantities are in direct proportion if dividing one by the other gives a constant value.

Indirect ProportionsTwo quantities are inversely proportional if their product is constant.