Characteristics of Science-part 1 CommonFolder/scienceindex.html

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

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

Designing an Experiment

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)

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

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)

Conducting the Experiment Record data carefully Note any mistakes or problems NEVER throw out “bad” data! It may be the most important part!!!

Selection & Use of Tools Tools *Proper use *Safety Characteristics of Science-part 2

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

Select the best tool Range –Too large – inaccuracies for small units –Too small – requires multiple measurements (more error)

Safety! –Chemicals ProjectilesProjectiles –Glassware »Flames »Heat »Fumes

Protective Gear Goggles Goggles are a must! –Spills/splashes; Projectiles; Fumes; shattered glass Lab aprons Lab aprons –Spills

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

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

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

Emergency procedures – just in case….. Shower Eye Wash Fire Extinguisher Fire Blanket

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!

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

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

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

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.

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

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

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

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

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