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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 Inquiry Work?
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 to test 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 Dependent variable
Example: Does the drop height affect the bounce height of a superball? We know the drop heights we will use. Dependent variable 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 ← a tentative answer to some question.
Figure 1.18


20 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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