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York University
Natural Science
NATS 1840
Carl Wolfe

NATS 1840LECTURE NOTESSEPT 13 2011 Environmental ScienceThinking UNIT 1 EnvironmentEverything that surrounds you from just outside your skin to the edge of the universeThe environment consists of all those parts of the physical world that help to sustain life o If a part of the environment is under stress a change then its ability to sustain life may be threatenedEnvironmental ScienceThe study of how the environment works and of humanitys impact upon it o A science o Interdisciplinary draws upon many varieties of science knowledge o Both theoretical and applied science understand the changes that take place and the causes of the changeScienceThe systematic study of how and why nature works the way it doesUses empirical methods testing ones offered explanations to test possible explanations of observationsSeeks to uncover basic underlying principles so that predictions may be made A rational process drawing upon two forms of reasoning o Inductive reasoningsynthesis creativity inspiration and imagination o Deductive reasoninglogic selfconsistency rigour mathematicsInduction Reasoning Based on ExperienceThe mode of thinking used in the formation of a hypothesisGeneral conclusion from limited number of observationsSynthesis of many observationsBottomup approach starts with observationsLimited by finite number of observationsnot logically valid o Inductive conclusions can only be proved in the sense that they are very likely but not guaranteed to be true Ex All objects ever observed fall to the ground when dropped Therefore all objects fall to the ground Deduction Logical ReasoningCrucial in analyzing the consequences of a hypothesisSpecific conclusions drawn logically from a generalizationConclusions are reliable at least internallyA topdown approachLimited by quality of assumptions o Deductive conclusion only as good as its premises o Although logically valid any deductive conclusion based on incorrect premises is invalid1 The Scientific MethodBased mainly on inductive reasoning and observationsDeductive reasoning crucial for designing tests usually called experiments o Observations o Questions o Hypothesis o Test hypothesisdo an experiment o Critically evaluate the results of the test o Determine if hypothesis is supported or contradicted o Disseminate 5 and 6 usually in a refereed peer reviewed publicationHypothesis disproved question still remainsHypothesis supported deductive consequences of that hypothesis must be tested What is a good scientific statementA hypothesis must be falsifiable can be disproved at least in principle Examples o The moon is made of cheese o Cell phones cause brain cancer o Suns energy source is nuclear fusionA hypothesis that cant be falsified is untestable isnt a scientific statement o GodAfterlife o Before the Big Bang o Some conspiracy theories example UFOThe Hierarchy of Scientific StatementsHypothesis o Tentative answer to a question ie an assumption o Weakest scientific statementTheory obased on inductive ideas experiments are made through deductive reasoning o A hypothesis or set of hypotheses that has survived many tests o More robust than a hypothesis in that there is greater confidence that it is rightLawo A theory that has passed so many tests that it is considered a fact o Observation seen so often that it becomes a fact o Most robust of all scientific statementsScientific ExperimentsTo be a useful test of a hypothesis can experiment must be o Controlled o Statistically significant o RepeatableAbsence of one or more of these criteria means a flawed experiment whose results shouldnt be trusted until they have been reproduced by a reliable experiment2Controlled experimentsMany variables may influence the outcome of an experimentOutcome of a controlled experiment depends on only one variableControl Group Subject Group Common Experiment Group 2 Group 1 many variables Act on one variable Observe ResponsesGroup 2 Group 1Any difference in response between subject and control must be due to the single different variable NATS 1840 LECTURE NOTESSEPT 15 2011 Environment ScienceThinking UNIT 1Statistical SignificanceScientific UncertaintyThe outcome of any measurement is characterized by o Accuracyhow close the outcome if to the true value o Precisionthe degree to which repeated measurements yield the same valueUncertainty in a measurement describes the range within which the true value most likely lies o For instruments ruler thermometer uncertainty is one half of the smallest division on the scale o Uncertainty in the average of several measurements decreases with the number of measurements in sampleN10 uncertainty 31N100 uncertainty10Statistical SignificanceControlled experiment with N1 and N2 controls or measurements Averages differ and have some uncertaintyIs the difference real Or just the result of random choice o To be statistically significant the difference in the averages must be greater than the error rangesRandom fluctuations might mimic a real response in a controlled experiment Statistical significance ensured by o Conducting experiment with many subjects and controls o Repeating several timesRepeatability 3
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