Chapter 3 Scientific Method

Two Types of Measurements They are either Qualitative or Quantitative. Qualitative Measurements are descriptions. For Example: The grade was a C+ Quantitative Measurements are numerical descriptions. For example: The grade is a 79.4.

Uncertainty in Measurements Accuracy and Precision Accuracy is how close you come to the actual “target” value of what you are measuring. The better the tool, the more accurate a measurement Precision is how close your measurements are to each other.

The Doubtful Digit Every measurement has a “doubtful digit” or estimated number This is always the last digit in a measured number. Reflect back to the ruler activity where you had to estimate…

Significant digits All numbers in a measurement including the doubtful digit. Tells others how accurate your measurements where based on the tool. You can’t just add decimals or numbers to a measurement

Significant Digits See handout for rules of counting. Practice! And rules for rounding them!

Rules for rounding If the digit to the right of last sig.dig is less than 5 do not change last sig dig If the digit to the right of the last sig dig is greater than five, round up the last sig dig. If the digit to the right of last sig dig is equal to five and followed by nonzero digit round up last sig dig

Cont, If the digit to the right of the last sig digit is equal to five and NOT followed by a nonzero digit, look at the last sig dig. If it is odd, round it up; if is even do not round!

Calculating Your answer can’t have any more sig digits than the least accurate (think ruler lab) of your tools!

Metrics Know the prefixes and the numbers: Kilo Hecto Deka m Deci centi milli “King Henry Doesn’t Milk Dairy Cows Mondays.” or “Kangaroos have dark mittens during cold months” Just Move the decimal to convert!

Factor label/Dimensional Analysis This is a Guaranteed Method of solving problems in Chemistry and Physics. Save yourself a lot of trouble and learn it well NOW! It uses units as labels and guides to your numbers Based on “conversion factors”-two things that are equal in amount i.e. 2.54 cm in 1 inch.

Percent Error A formula for determining just how close you are to accuracy % E = (true value) – (exp. Value) x100 (true value)

Density Density is a physical property of a substance. It is a ratio of mass and volume and does NOT depend on the size of the sample Density of water = 1.00 g/ml “Less dense Floats. More Dense sinks”

Formula Density = Mass/ volume