Chapter 1, Section 3: Pages 10 to 13

What is the scientific method? A systematic approach to problem-solving.

What are the steps of the scientific method? Observation – identify a problem.Observation – identify a problem. Form hypothesis – possible explanation.Form hypothesis – possible explanation. Experiment – to test the hypothesis.Experiment – to test the hypothesis. Conclusion: revisit hypothesis. Does it need to be adjusted?Conclusion: revisit hypothesis. 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 Observations Use words to describe – the color, odor, shape, texture, or some other physical characteristic.

Quantitative Observations Use numbers to describe a property. Result from measurement. Include a number and a unit. –Height, Mass, Temperature

What’s the difference between a fact and an inference? FactsFacts can be verified. They are objective. InferencesInferences are subjective. They involve conclusions drawn from data. –On Friday the 13 th I saw a black cat. –On Friday the 13 th I saw a spooky cat.

Facts vs. Inferences Ice Floats. (Observed fact.) Ice must be lighter than water. Only things lighter than water will float. Careful!Careful!

Experiments variablesMost systems in nature have many variables. (Parameters that can change.) An experiment is an attempt to simplify nature. constant –Hold most variables constant. Independent variable –Manipulate one variable. (Independent variable. Controlled by the scientist.) Dependent variable –Measure one variable. (Dependent variable.)

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 of scientific method. 1Theory (model) 1 - Theory (model) 2 – Law (summary)

Theory 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 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 between a theory and a law again?

Theory vs. Law Attempt to explain why something happens. Summarizes what always 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

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.