Experimental Design

Purpose/Objective

• Statement of the problem or question to be answered

• Usually this involves an observation of some type of phenomenon

• What is the difference between an observation and an inference?

Observation vs. Inference?

When Ms. Moracco comes home from school, her dog Chesney’s tail is moving back & forth. He jumps up & down, barking rapidly. He is happy to see her.

Background/Research

Information already known or researched

Should come from RELIABLE sources (e.g. wikipedia is not an example - ever in this classroom!!!)

Hypothesis

• Testable statement which may be falsified• Written as if…then statement where the

independent variable follows the if and the dependent variable follows the then.

• Independent variable- The factor/condition being tested or changed purposely by the experimenter

• Dependent Variable- the factor/condition being measured or that changes as a result of the independent variable

Misconception Alert!!!

Hypothesis Educated

Guess

Experiment

• Materials- list of all equipment necessary • Procedure - step-by-step description of

how to the experiment…should be reproducible by anyone wishing to replicate your results.

Experiment Con’t.

• Constants- factors/conditions that are kept the same in both the experimental and control groups

• Control Group- “normal”/non tested group; standard for comparison; Nothing is done to this group

Example

• How bright is right?• An automobile manufacturer wants to know how bright

brake lights should be in order to minimize the time required for the driver of a following car to realize that the car in front is stopping and to hit the brakes.

• What is the independent variable? • (brightness of brake light) • What is the dependent variable? • (time to hit brake)

Data

• Qualitative - categorical; warm & fuzzy; not reproducible (e.g. blue, hot, cold)• Quantitative - direct measurements with

correct units (e.g. temperature, time, distance)

Analysis

• A detailed record of all observations (data tables, graphs, etc.) & a summary or explanation of those observations

Conclusion

• A final statement of whether or not the original hypothesis was supported or not

• Evaluation of human error…In other words what did you do wrong?

• Then what?

Facts, Proof, Theories & Laws

• Fact: Observation confirmed over & over (change more often than theories!!!)

• Proof: NOTHING in science is proven. This word does not belong in science. Send this word to your math teacher!

• Theories are an explanation of a natural phenomenon that is supported by a large body of scientific evidence obtained from many observations, experiments and laws.

• A law is a generalized description of a fact of nature about what has happened from which we can generalize what we think will happen or how something behaves under certain circumstances. E.g. An apple falls to the Earth because of the Law of Gravity.

Misconception Alert!!!!

Theory Law

Revisiting Theories

Theories are explanations - look at the diagram……

Facts

Laws

Inferences

Tested hypotheses

Explanation

Theories vs. Laws - quick review

Theories are Laws are

Based on evidence Based on evidence

Tested Tested

Effective in Problem SolvingExplanation of how Explanation of what

will happen

Words of Experimental Design

Observation/Inference Hypothesis Procedure Constant Control Variables (two kinds) Data (two kinds) Fact Hypothesis Law Theory