The International System (SI) Uses the Metric System to describe quantitative (measured) properties of matter rather than qualitative (non measured) characteristics Metric System Uses a set of standard base units for measuring Conversions between base units are easily calculated Prefixes are added to base units to obtain smaller or larger quantities Works using powers of ten (10n)

Mass Measure of the quantity of matter present against a standard Weight Measure of the force of gravity on an object Example On Earth a led ball has a wt. Of 8 kg. When taken to the moon it has a wt. of 1kg. Does the amount of matter (lead) change? The difference in weight is due to gravity. The mass does not change

Temperature U.s. uses Fahrenheit (oF) degrees SI uses Kelvin (K) in calculations but measures in Celsius (oC) degrees K = oC + 273 oC = K – 273 oC based on properties of water Freezes at 0oC Boils at 100oC HW read pgs.24-30 pg.30 # 4,5 and 7-11

Scientific Notation Expresses numbers as multiple of two factors One whole number to left of a decimal point Ten raised to a power or exponent Exponent tells how many times the number is multiplied by 10

Adding and subtracting scientific notation Make powers the same exponent Add or subtract numbers Retain the power of 10 (exponent)

Multiplying and Dividing using Scientific Notation Multiply or divide the numbers If multiplying: add exponents If dividing: subtract exponents Readjust for proper notation HW read pgs. 31-33 pg.32 #12-14 pg.33 #15-16

Accuracy and Precision How close a measurement is to the true or actual(correct,targeted) value for the quantity Being exact Precision How close a set of measurements for a quantity are to one another, regardless of whether the measurements are correct Allowable tolerance or deviation

Examples Measure boiling water three times with same thermometer The following measurements are recorded 97oC, 97oC, 97oC Since the data are not 100oC the measurements are not accurate, but they are consistent and close so they are precise A different thermometer records 100oC, 100oC, 100oC Since the measured values are all correct, the measurements are accurate Note: accurate measurements are also precise

Percent Error Shows the deviation of collected experimental(exp) data(measurements) to a given or true value Percent error = experimental value – accepted value x 100 accepted value Negative value shows too little Positive value shows too much Actual error = exp. – true HW Read pgs.36-38 pg.38 #29-30

Significant figures All digits that occupy places for which an actual measurement was made Used in calculations In multiplication and division the result must be reported with the same number of sig figs as the measurement with the fewest sig figs In addition and subtraction the result cannot have more digits to the right of the decimal point than any of the original numbers HW Read pgs. 38-39 do worksheets