Observing, Measuring, & Calculating Chapter 1

Scientific Method https://www.brainpop.com/science/scientif icinquiry/scientificmethod/ Problem/Question – Observe a problem and ask a question. Research - Conduct background research. Write down your sources so you can cite your references. Hypothesis - Propose a hypothesis. This is an educated guess about what you expect.

Scientific Method cont. Experiment - Design and perform an experiment to test your hypothesis. Data/Analysis - Record observations and analyze what the data means. Often, you'll prepare a table or graph of the data. Conclusion - Conclude whether to accept or reject your hypothesis. Communicate your results.

Observing Physics and Chemistry *Qualitative observation – observation made without measurement *Quantitative observation – observation made through measurement

Measuring *Measurement is used to quantify matter *Must be accurate (correct) *Must be precise (repeatable) Neither accurate nor precise Precise, but not accurate Precise AND accurate

Measuring cont. Accurate measurements *Rule: Measure what you know “for sure” plus one estimated digit *2 cm? 2.4 cm? 2.45 cm? *More significant digits = more accuracy 1 2

Measuring cont. *The accuracy of your measuring device determines the accuracy of your measurement *How accurate can the above measurement be? 1 2 3

Which is the most accurate measurement?

Rounding calculations Decide how many digits are needed Round to that many digits, counting from the left Is the next digit less than 5? Drop it. Next digit 5 or greater? Increase by 1

Rounding calculations, cont. 1. Addition and Subtraction The answer should be rounded to the same number of decimal places as the least number of decimal places in the problem ex/ 6.8 + 11.934 = 18.734  18.7

Practice… Calculation Calculator says: Answer 3.24 m + 7.0 m 10.24 m 100.0 g - 23.73 g 76.27 g 76.3 g 0.02 cm + 2.371 cm 2.391 cm 2.39 cm 713.1 L - 3.872 L 709.228 L 709.2 L 1818.2 lb + 3.37 lb 1821.57 lb 1821.6 lb 2.030 mL - 1.870 mL 0.16 mL 0.160 mL *Note the zero that has been added.

Rounding calculations, cont. 2. Multiplication and Division Round the answer to the same number of digits as the least number of significant figures in the problem. ex/ 6.38 x 2.0 = 12.76  13 (2 sig figs)

Practice… Calculation Calculator says: Answer 3.24 m x 7.0 m 22.68 m2 100.0 g ÷ 23.7 cm3 4.219409283 g/cm3 4.22 g/cm3 0.02 cm x 2.371 cm 0.04742 cm2 0.05 cm2 710 m ÷ 3.0 s 236.6666667 m/s 240 m/s 1818.2 lb x 3.23 ft 5872.786 lb·ft 5870 lb·ft 1.030 g x 2.87 mL 2.9561 g/mL 2.96 g/mL

Density Density = The formula for density is: mass volume Common units are: g/mL, or g/cm3, (or g/L for gas) Density is a physical property, and does not depend upon sample size Density =

The Metric System System of base units and prefixes Based on powers of 10 Base units Length – meter (m) Mass – gram (g) Volume – liter (l) *note 1 cm3= 1ml water

Prefixes Mega M 106 Kilo k 103 Base unit 0 Centi c 10-2 Milli m 10-3 Micro  10-6 Move decimal to right Move decimal to left

Metric conversions Convert 560 mL to L Convert 4.25 km to mm Convert 2,200 um to m Convert 0.023 cg to kg

Dimensional Analysis *A method of problem-solving using conversion factors Conversion Factor *Is essentially an equality ex/ 12 inches = 1 foot *Is written as a ratio to cancel units 12 inches OR 1 foot 1 foot 12 inches

Dimensional Analysis Problems 1. Convert 15 feet to inches. 2. Convert 176 inches to yards.

Dimensional Analysis, cont. 1. Convert 2,500 inches to yards. 2. Convert 0.0034 miles to inches.