The Scientific Method

Scientists solve problems in two ways A. Descriptive Research B. Experimental Research

Descriptive Research There are many instances in science when an experiment cannot be done or not necessary to answer a question or problem. Ex. How long does it take Saturn to orbit the Sun? This type of research is based on observations.

For example How could you describe these objects using words and numbers?

Experimental Research This method answers scientific questions or problems by observation of a controlled situation called an experiment. The scientist collects data and analyzes the results to form a conclusion.

When doing experiments, scientists must: choose the correct equipment use the correct units of measurement Use the proper lab write-up format follow all lab safety rules

The Scientific Method There are 6 steps: Question or Problem Hypothesis Procedure and Materials Test the Hypothesis or Experiment Data and Results Analysis and Conclusion

Decide on what the problem is. Step 1: Ask a question OR Decide on what the problem is. Questions begin with WHAT, WHY, HOW, or WHEN.

How does acid rain affect plant growth? For Example: How does acid rain affect plant growth?

Step 2: Form a Hypothesis A hypothesis is a clear statement of what you EXPECT the answer to your question to be.

The hypothesis should be stated in an If-Then Format. For Example: If a plant is watered with only acid rain, then the plant will grow at half its normal rate.

I think that acid rain causes plants to grow more slowly. Do NOT use personal pronouns!! I, Us, We, They, Them Bad Example: I think that acid rain causes plants to grow more slowly.

Procedure and Materials Step 3: Procedure and Materials Write down step by step how the experiment is to be conducted including all materials and equipment needed.

You test your hypothesis by doing the experiment. Step 4: Test Your Hypothesis You test your hypothesis by doing the experiment.

Do Multiple Trials! When doing an experiment, perform each test several times. This is to ensure accurate results.

Data and Results Step 5: Write down all observations Record results from experiment in table, chart, graph or diagram

Tables and graphs are often useful in helping to organize the data. Every graph always needs a key so people can easily tell what each color or pattern represents.

Analysis and Conclusion Step 6: Analysis and Conclusion Analyze the information you have gathered in the experiment. Conclude whether the results support your hypothesis or refute it.

What is important is that you explain WHY you got the results you did. REMEMBER : It is NOT important for the hypothesis to be correct. What is important is that you explain WHY you got the results you did.

Variables A variable is a factor that could affect the outcome of an experiment. In a well-planned experiment, one factor or variable is changed at a time.

Independent Variable The independent variable is the variable that is changed in the experiment. The scientist changes it or controls it. Also known as the Manipulated Variable

Dependent Variable The dependent variable is the factor being measured. It changes as a result of the changes in the independent variable. Also called the Responding Variable

Controls The variables that stay the same are called constants. An experiment where there is only one independent variable and all other variables are kept constant is called a controlled experiment.

In an experiment, only one variable is changed at a time. This is done to ensure that the changes in the independent variable alone are responsible for any changes in the dependent variable (results).

For Example: Problem and Hypothesis Independent and Dependent Variable

For Example: Dr. Salk tested his vaccine for polio on thousands of people. He gave half of them the real vaccine and the other half a fake vaccine called a placebo. He found out that the people who had taken the real vaccine got better. His vaccine worked!! Independent Variable? Dependent Variable?