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Characteristics of Science-part 1 http://web2.newtown-h.schools.nsw.edu.au/Science/ CommonFolder/scienceindex.html
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Theory vs Law Theory Theory substantial evidence –Based on substantial evidence – an accepted hypothesis –Explains –Explains observed facts (how nature works) accepted –Generally accepted by the field –Provides a basis to build upon
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Law Then what is a Law? substantial evidence Also based on substantial evidence. what will happen Describes behavior of nature – what will happen Does not attempt to explain why Often follows a mathematical formula *Law of gravity*Avogadro’s Law *Charles’ Law*Newton’s Law of motion
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Designing an Experiment
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independentdependent Hypothesis should define your independent & dependent variables response Testing the response of the dependent variable to changes in the independent variable controlled variables Important to keep all other influences under control (controlled variables)
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Error vs Bias Experimental Error Experimental Error –Random - part of every experiment Minimize but cannot avoid entirely Measurement imprecision Sample variability Affects reproducibility –detected (and corrected for) by statistical analysis. Simplest form – average of many trials
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Avoiding Bias – it’s in the Design Control group (can’t compare apples to oranges) – ex: men vs women Method/Measurement ToolsTools – accuracy or sensitivity HumanHuman – awareness (white coat effect), memory, expectation (placebo effect)
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Conducting the Experiment Record data carefully Note any mistakes or problems NEVER throw out “bad” data! It may be the most important part!!!
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Selection & Use of Tools Tools *Proper use *Safety Characteristics of Science-part 2
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Select the best tool Accuracy – by design –Beaker vs graduated cylinder Precision – –*use the most precise tool available (minimizes error) –*use it correctly! 1 estimate past markings
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Select the best tool Range –Too large – inaccuracies for small units –Too small – requires multiple measurements (more error)
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Safety! –Chemicals ProjectilesProjectiles –Glassware »Flames »Heat »Fumes
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Protective Gear Goggles Goggles are a must! –Spills/splashes; Projectiles; Fumes; shattered glass Lab aprons Lab aprons –Spills
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Heat & Flames Avoid flames when possible – use other heat sources (oven, hot plate, etc) When unavoidable – WEAR GOGGLES – avoid dangling clothing, tie back hair chemistry.about.com
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Ewww that smell! Some fumes are unpleasant – others are dangerous! Use properly vented fume hood Room fan should also be available Proper chemical goggles can protect against fumes getting into eyes Protective mask under extreme conditions
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No Food or Drink No eating or drinking near lab area Always wash hands after handling chemicals or equipment Keep hands away from face & eyes
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Emergency procedures – just in case….. Shower Eye Wash Fire Extinguisher Fire Blanket
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Characteristics of Science-part 3 Analyzing Data Human error – a mistake Did not follow procedure Contaminated the sample Misread the instrument Calculations done incorrectly Can be eliminated with training & experience – time for a re-do!
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Sources of Error Random Experimental Error –No measurement can be made to infinite precision –Can be introduced by human – but unavoidable (ex – use of stopwatch) –Not a mistake – a limitation in the methodology –Impact removed by averaging multiple trials
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Sources of Error Systemic Error = Bias –Part of the experimental design Poor instrument Poor design –Must be avoided at all costs! Produces skewed data Always skewed in the same direction Reproducible error – wrong every time
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Analyzing Data Multiple trials – the more, the better Averaging data reduces effects of random error % Error used to assess accuracy of an experiment when a standard value is available: % error = (standard value –exp. value) x 100 standard value
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Analyzing Data Standard deviation - examines error more closely Reported as average ± S.D. Large S.D. = significant random error (possibly careless technique) Smaller S.D. = less random error – more careful technique “Overlap”- two measurements were not shown to be different.
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Analyzing Data Looking for trends Looking for trends - Graphing & slope DRY MIX –Dependent variable –Dependent variable on Y axis –Independent variable –Independent variable on X axis Positive (direct) correlation Negative (inverse) correlation rate of change Slope calculates the rate of change Rise over run
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Sharing of Data – an important part of developing a Theory or Law Function of the scientific community: To challenge – lead to revision of an hypothesis or theory To support – add to accumulating evidence in support of a theory
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Interpret with care! Done well - Leads to –revised hypothesis –more testing –Ultimately better understanding & a working theory Done poorly – Leads to –Misunderstanding/confusion –Often dangerous misconceptions
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Characteristics of Science-part 4 Models are a tool that describes connections between multiple systems. provides a simplified explanation may be used to predict can be applied to many similar situations
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Models: Their Advantages & Limitations Advantages Advantages –Easily understood –Apply to many areas –Communication/teaching tools Disadvantages Disadvantages –It’s not always that simple! Ex: Bohr’s model of the atom vs Quantum theory
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