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Scientific Method

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Steps in the Scientific Method Observation Observation Hypothesis Hypothesis Experiment Experiment Data Collection Data Collection Conclusion Conclusion Retest Retest

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Observations Gathered through your senses Gathered through your senses A scientist notices something in their natural world A scientist notices something in their natural world

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Observations An example of an observation might be noticing that many salamanders near a pond have curved, not straight, tails An example of an observation might be noticing that many salamanders near a pond have curved, not straight, tails

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Hypothesis A suggested solution to the problem. A suggested solution to the problem. Must be testable Must be testable Sometimes written as If…Then… statements Sometimes written as If…Then… statements Predicts an outcome Predicts an outcome

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Hypothesis An example of a hypothesis might be that the salamanders have curved tails due to a pollutant in the moist soil where they live. An example of a hypothesis might be that the salamanders have curved tails due to a pollutant in the moist soil where they live.

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Experiment A procedure to test the hypothesis. A procedure to test the hypothesis.

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Experiment Variable – factor in the experiment that is being tested

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Experiment A good or “valid” experiment will only have ONE variable!

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Controls and Variables

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Scientific Experiments Follow Rules An experimenter changes one factor and observes or measures what happens.

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The Control Variable The experimenter makes a special effort to keep other factors constant so that they will not effect the outcome. The experimenter makes a special effort to keep other factors constant so that they will not effect the outcome. Those factors are called control variables. Those factors are called control variables.

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What is the Purpose of a Control? Controls are NOT being tested Controls are used for COMPARISON

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Other Variables The factor that is changed is known as the independent variable. The factor that is measured or observed is called the dependent variable.

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Example of Controls & Variables For example, suppose you want to figure out the fastest route to walk home from school. You will try several different routes and time how long it takes you to get home by each one. Since you are only interested in finding a route that is fastest for you, you will do the walking yourself.

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What are the Variables in Your Experiment? Varying the route is the independent variable Varying the route is the independent variable The time it takes is the dependent variable The time it takes is the dependent variable Keeping the same walker throughout makes the walker a control variable. Keeping the same walker throughout makes the walker a control variable.

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One more thing… it is best to make several trials with each independent variable.

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Valid Experiments

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Remember: To be a Valid Experiment: Two groups are required --- the control & experimental groups There should be only one variable

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Data Results of the experiment May be quantitative (numbers) or qualitative

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Data Must be organized Can be organized into charts, tables, or graphs

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Conclusion The answer to the hypothesis based on the data obtained from the experiment

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Retest In order to verify the results, experiments must be retested.

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Measurement Scientific investigations usually require measurements. All scientists use a consistent measurement system; SI (System International) or the metric system

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Units of Metric Measurement Length: linear distances Millimeter (mm); centimeter (cm); meter (m); kilometer (km) Mass: the measure of how much matter something has Matter is defined as anything that takes up space and has mass Gram (g); kilogram (kg); metric ton

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Units of Metric Measurement Volume and area: Area is the amount of surface within a set of boundaries; square units of length (m 2 ) Volume is the amount of space occupied by an object; depends on the type of object Solids are measured in cubic units (m 3 ) Liquids are measured in milliliters or liters; mL or L.

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Units of Metric Measurement Density: the measure of the amount of matter that takes up a certain space Mass divided by volume Grams per cubic centimeter (g/cm 3 ) Time: measured in seconds or minutes Temperature: usually in Celsius Kelvin is the official SI unit for temperature Absolute zero is -273 o C or 0K

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Review

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Solving a Problem 1)Identify a Problem 2) State Observations about the problem 3) Form a Hypothesis about the problem (if…then…) 4) Design an Experiment to test the hypothesis 5) Collect Data 6) Form a Conclusion 7) Retest

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Learning Targets Compare and contrast independent and dependent variables. Discuss the parts of the scientific method Discuss the units of the metric system

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