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Introduction to Experimental Design

Introduction to Experimental Design. AP Biology. Science. A way of learning about the natural world Includes all of the knowledge gained by exploring the natural world This knowledge is always growing and changing as scientists ask new questions and explore new ideas.

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Introduction to Experimental Design

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  1. Introduction to Experimental Design AP Biology

  2. Science • A way of learning about the natural world • Includes all of the knowledge gained by exploring the natural world • This knowledge is always growing and changing as scientists ask new questions and explore new ideas

  3. Scientific Inquiry • Scientific: Of or relating to the practice of science • Inquiry: A close examination of a matter in a search for information or truth • Scientific Inquiry: The ways in which scientists explore the natural world

  4. How Does Scientific InquiryWork? • Scientific Method: • Make observations and/or inferences • Ask questions • Develop hypotheses • Design experiments • Make measurements • Collect data • Interpret data • Draw conclusions • Communicate

  5. Make Observations and Inferences • Observation: Using one or more of your senses to collect data • Inference: An interpretation of an observation that is based on evidence or prior knowledge • Data: Facts, figures and other evidence gathered through observation

  6. Question • You ask a question about what you observe. • State the problem or question. • Example: Does the drop height affect the bounce height of a superball?

  7. Developing a Hypothesis • Hypothesis: A possible explanation for a set of observations or answer to a scientific question • A hypothesis must be something that can be tested • Worded as an If . . . Then statement • Hypotheses can either be supported or disproved • Example: If a superball is dropped from increasing heights then the bounce heights will also increase because…

  8. Null Hypothesis • A hypothesis that can be rejected-it essentially states that the variables will have no effect on the outcome of the experiment • Why use a Null Hypothesis? • You can never have enough support for a hypothesis to say that it is the sole explanation of a phenomenon, but you can have enough data to show that it is not the sole explanation of a phenomenon.

  9. Designing an experiment totest a hypothesis • After you state your hypothesis, you must design an experiment to test it. • You figure out a way to test whether the hypothesis is supported. • Control group– nothing changed • Experimental group – one variable changed • The outcome must be measurable (quantifiable). • Record and analyze data.

  10. Designing a Controlled Experiment. • An experiment in which all of the variables except for one are remain the same • An experiment that is designed to compare an experimental group with a control group. • Ideally, a control group and an experimental group differ in only one variable. • Control group serves as a comparison to measure against

  11. Experiment Variables • Variable: Factors that can change in an experiment • Manipulated (Independent) Variable: The variable that is changed during the experiment • Responding (Dependent) Variable: The factor that changes because of the manipulated variable • Variable that is measured in the experiment

  12. Variables • Independent variable • Example: Does the drop height affect the bounce height of a superball? • We know the drop heights we will use. • Dependent variable • Example: Does the drop height affect the bounce height of a superball? • We don’t know the bounce height before we start. It is what is being measured.

  13. Constants • Constant: a variable that does not change for the duration of an experiment; a value that remains the same • Examples: Does the drop height affect the bounce height of a superball? • The superball does not change during the experiment. The same force is applied during each trial.

  14. Interpreting Data • You do the experiment using the method you came up with and record the results. • After the data are collected, they must be organized and interpreted • Create data tables, graphs to represent data • Perform calculations that will determine what results mean (averages, percentages, totals) • Identify possible sources of errors

  15. Drawing Conclusions • After you have organized and interpreted your data, you must draw a conclusion. • You need to decide if the data support your original hypothesis.

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

  17. Communicating • Scientists must communicate their findings to other scientists. • This contributes to the growth of the body of • scientific knowledge.

  18. Scientific Theories • Scientific Theory: A well-tested concept that explains a wide range of observations. • A theory is based on thousands of experiments done by different scientists. • A theory is much broader in scope than a hypothesis. • Theories only become widely accepted in science if they are supported by an accumulation of extensive and varied evidence. • Future testing may prove a theory to be incorrect.

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