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Chapter 2

Chapter 2. Scientific Method. Scientific Method. Scientific method- logical approach to solving problems by observing & collecting data, formulating hypotheses, testing hypotheses, formulating theories supported by data Examples of problems… Observable data

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Chapter 2

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  1. Chapter 2 Scientific Method

  2. Scientific Method • Scientific method- logical approach to solving problems by observing & collecting data, formulating hypotheses, testing hypotheses, formulating theories supported by data • Examples of problems… • Observable data • Qualitative = descriptive (turn pink) • Quantitative = numerical (1 gram)

  3. Data • We cannot observe everything all at once, so we focus on a system • System- specific portion of matter chosen for study (ex. Reaction in a test tube) • Once we obtain data, we can establish patterns • Patterns can be made into scatter plots, bar graphs, pie charts, etc.

  4. Hypothesis • Once we have looked for patterns, we form a hypothesis • Hypothesis- testable statement in the form of “if…then…” • Then we have to test the hypothesis • Control(s)- stay constant (placebo) • Variable(s)- change, only changed one at a time • If wrong, change or drop hypothesis (might start over)

  5. Hypothesis (con.) • If correct, explain through models • Model- explains how events occur or are related in a visual, verbal, or mathematical way • Theory- broad generalization that explains group of facts or events • Publish results (letters, scholarly journals, blog, word of mouth)

  6. Metric System • SI, or SystèmeInternationaled’Unités (French) • Base units • Length (lowercase L) = meter (m) • Mass (m) = kg (kilogram) • Time (t) = second (s) • Temperature (T) = Kelvin (K) • Amount of substance (n) = mole (mol) • Electric current (I) = ampere (A) • Luminous intensity (Iv) = candela (cd)

  7. Metric prefixes • Mega (M) = 10 6 • Kilo (k) = 10 3 • Hecto (h) = 10 2 • Deka (da) = 10 1 • Deci (d) = 10 -1 • Centi (c) = 10 -2 • Milli (m) = 10 -3 • Micro (µ) = 10 -6 • Practice problems on board

  8. Mass vs. Weight • Mass = amount of matter • Weight = amount of gravity pull • On moon, gravity 1/6 that of Earth • Didn’t lose mass, lost weight

  9. Derived SI units • Combinations of base units • Area (A) = lxw = m2 or cm2 • Volume (V) = lxwxh = m3 or cm3 • Density (D) = kg/m3 or g/cm3 or g/mL • Molar Mass (MM) = kg/mol • Energy (E) = Joule (J)

  10. Accuracy vs. Precision • Accuracy- close to accepted value • Precision- close to measurements made in same way • Drawings on board

  11. Percent Error • Goal = 0 • (Experimental – Accepted)/(Accepted) x 100 • Problems on board

  12. Significant figures • All digits but last one certain • Rules • Nonzero = significant • Zero in between nonzero (2002) = significant • Zero in front of nonzero = not significant • Zero at end of number and to right of decimal = significant • Ex. 2000 = 1 sig, 25.00 = 4 sig, .0001 = 1 sig • Examples on board

  13. Rounding • 1->4, round down • 6->9, round up • 3.5->4 • 4.5->4 • Sig + or – Sig= same # of decimals • Sig x or / Sig = same # of sig digits • Examples on board

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