Chapter 1, Section 3: Pages 10 to 13

What is the scientific method?

A systematic approach A systematic approach to problem-solving.to problem-solving.

What are the steps of the scientific

method?• Observation – identify a Observation – identify a problem.problem.

• Form hypothesis – possible Form hypothesis – possible explanation.explanation.

• Experiment – to test the Experiment – to test the hypothesis.hypothesis.

• Conclusion: revisit hypothesis. Conclusion: revisit hypothesis. Does it need to be adjusted?Does it need to be adjusted?

Hypothesis

• Testable, educated guess to explain an observation.

Experiment

• Set of controlled observations to test the hypothesis.

Hypothesis

Observations

Experiments Theory

Scientific Law

Observations are facts you take in with

your senses. They can be

•QualitativeQualitative•QuantitativeQuantitative

Qualitative ObservationsQualitative Observations

•Use words to describe– the color, odor, shape, texture, or some other physical characteristic.

Quantitative ObservationsQuantitative Observations

• Use numbers to describe a property.

• Result from measurement. • Include a number and a unit.

– Height, Mass, Temperature

What’s the difference What’s the difference between a fact and an between a fact and an

inference?inference?• FactsFacts can be verified. They are

objective.• InferencesInferences are subjective. They

involve conclusions drawn from data.– On Friday the 13th I saw a black cat.– On Friday the 13th I saw a spooky cat.

Facts vs. InferencesFacts vs. Inferences

• Ice Floats. (Observed fact.)

• Ice must be lighter than water.

• Only things lighter than water will float.

• Careful!Careful!

Experiments• Most systems in nature have many variablesvariables.

(Parameters that can change.)• An experiment is an attempt to simplify nature.

– Hold most variables constantconstant.– Manipulate one variable. (Independent Independent

variablevariable. Controlled by the scientist.)– Measure one variable. (DependentDependent

variablevariable.)

Control

• Control: Perform the experiment under specific conditions. Standard for comparison.

• Compare the experiment with the control. They should differ by only 1 variable.

Conclusion

• Judgment based on the experimental data.

• Does the experiment confirm the hypothesis or does the hypothesis need to be modified?

2 Long-term outcomes 2 Long-term outcomes of scientific method.of scientific method.

• 11 - Theory (model)Theory (model) • 2 – Law (summary)2 – Law (summary)

Theory or ModelTheory or Model•an overall explanation of

some natural phenomenon. • Ex: Kinetic Theory.

– Supported by many experiments – explains lots of observations

– Can be modified– Can be used to make predictions

Some Theories

• Kinetic Theory• Theory of Natural Selection• Theory of Relativity

Scientific LawScientific Law

•Summary of accepted facts of nature.–Law of Conservation of Energy–Law of Conservation of Mass –Law of Conservation of Charge.

What’s the difference What’s the difference between a theory between a theory and a law again?and a law again?

Theory vs. LawTheory vs. Law

Attempt to Attempt to explain explain whywhy something something happens.happens.

Summarizes Summarizes whatwhat always always happens.happens.

Ozone - Observations

• 1970’s: scientists observed the presence of CFCs in the atmosphere.

• 1980’s: scientists observed thinning of the ozone layer over Antarctica.

Ozone - Hypothesis

• Chlorofluorocarbons (CFCs) are responsible for the thinning of the ozone layer.

Ozone - Experiments

• Many photochemical and kinetics experiments of ozone and CFCs.

• Proposed model:

Ozone & CFCS

• Sunlight breaks down CFCs in the atmosphere.

• Breakdown products destroy ozone.

Step 1: Formation of ozone

Formed in the upper stratosphere.

Mostly stored in the lower stratosphere.

Chlorofluorocarbons

• Contain carbon, fluorine, and chlorine.

• Used as refrigerants, as propellants in spray cans, and in plastic foams.

• Do not occur in naturally.

NASA simulation

NASA simulation

Judgment

• Do the experiments confirm the hypothesis or contradict it?

Prediction

• Decreasing the amount of CFC’s in the upper atmosphere will slow the destruction of the ozone layer in the upper atmosphere.