Physics 8/26/2015 Objective: – Identify metric prefixes and their meaning – Convert between scientific and standard notation – Make measurements with accuracy – Record data using SI units Vocab: Scientific notation, significant figures, metric prefix Bell Question: When was a time you had to measure something very accurately? What were you doing? What unit were you using? Homework: Finish worksheets if you don’t finish in class

Measurements and Calculations Chapter 2

Units of Measurement Measurements involve NUMBER and UNIT Represent a quantity: has magnitude, size, or amount Gram = unit of measurement Mass = quantity

Units of Measurement Scientists around the world agree on one system… – International System of Units (le Systeme International d’Unites) – SI units – Built from seven base units

SI Base Units Length – Unit: meters Symbol: mTool: ruler Mass – Unit: kilogramsymbol: kgtool: scale Time – Unit: secondssymbol: stool: watch

Derived Units Are made when we combine units together.

Units of Measurement Metric Prefixes – make units easier to use Make the unit smaller or larger Unit = prefix + base unit

Scientific Notation Put the numbers in the form a x 10 n a has one # to left of decimal If # is bigger than 1  + exponent If # is less than 1  - exponent

Scientific Notation Review: Write in scientific notation 32, x x 10 8

Significant Figures (sig figs) How many numbers mean anything? When we measure, we can (and do) always estimate between the smallest marks

Significant figures (sig figs) Better marks better estimate. Last number measured actually an estimate 21345

Sig Figs What is the smallest mark on the ruler that measures cm? 142 cm? 140 cm? Does the zero mean anything? (Is it significant?) They needed a set of rules to decide which zeroes count.

Rules of Sig Figs 1) ALL non-zero numbers (1,2,3,4,5,6,7,8,9) are ALWAYS significant. 2) ALL zeroes between non-zero numbers are ALWAYS significant. 3) ALL zeroes which are to the right of the decimal point AND at the end of the number are ALWAYS significant. 4) ALL zeroes which are to the left of a written decimal point and are in a number >= 10 are ALWAYS significant.

Easier Way to do Sig Figs!! Pacific/Atlantic PA If a decimal point is present, start on the Pacific (P) side and draw an arrow through the number until you hit a non-zero digit. Count all numbers without an arrow through them. If a decimal is absent, start on the Atlantic (A) side and draw an arrow through the number until you hit a non-zero digit.

Examples: grams decimal present, start on “P” side, draw arrow, count digits without an arrow through it. Answer = 6 10,100 centimeters Decimal absent, start on “A” side, draw an arrow, count digits without an arrow through it. Answer = 3

Now practice on your own! How many sig figs are in the examples on your paper?

Sig Figs Only measurements have sig figs. Counted numbers are exact – infinite sig figs A dozen is exactly 12

Rounding rules Round to four sig figs – to three sig figs – to two sig figs – to one sig fig

Lab Directions: Take measurements at each station – 3 different people measure – did you all get the same thing? Find the average of your measurements (add together and divide by 3) Do the conversion problems in the second table