SCIENTIFIC METHOD

Designing an experiment
If someone says that they are going to experiment on you, right away you know that they are going to use you as a guinea pig. They are going to do something to you. You are part of the experimental group. However, in order for them to know if what they are doing to you really works, they need to compare you to someone whom they did not experiment on. This person would be the control group.

An experiment always consists of an experimental group and a control group.

The experimental group is the group receiving the treatment, or the group that something is being done to.

The control group does not receive the treatment. The control group is the standard for comparison. The control group is not experimented on.

When you are asked to design an experiment, you should write down the questions that you are trying to answer. That is the problem.

Your hypothesis is what you believe is going to happen and this statement should be generated based on some previous experience or research on this topic. The hypothesis should be carefully written to answer the questions and also formatted in a way, which can be tested. This can be done by saying what you are going to do and what you expect to happen as a result of what you do. For example, what is the effect of increasing physical activities on pulse rate? HYPOTHESIS:  If you increase your physical activities, then your pulse rate will increase.

NOTE: A well written hypothesis always consist of an independent and a dependent variable.

The dependent variable is what is being observed or measured. In this case, the dependent variable is the pulse rate.

The independent variable is the treatment or the only factor in an experiment that can be manipulated or changed. In this case, the independent variable is increasing physical activities.

ANOTHER WAY OF LOOKING AT THINGS is cause and effect. The independent variable is the cause and the dependent variable is the effect.

NOTE The dependent variable depends on the independent variable. The independent variable you know before the experiment and the dependent variable you find out after the experiment.

OBSERVATION: Probably is the most important step in the scientific method. We observe using our five senses. (Sight, taste, smell, touch and hear).

The experiment is a test of the hypothesis.


Data is information that is collected during the experiment. 

We analyze data after the experiment by looking for patterns using graphs, tables and charts,

Conclusion is an explanation of the data. (after the experiment)

Inference: A conclusion based on observation or evidence.

Theory is a hypothesis that is supported by many experiments or a broad explanation of natural events that is supported by strong evidence of repeated experiments.



The characteristics of a good experiment

• In an experiment, the sample size should large (test many subjects) to make up for genetic differences of other inconsistencies.
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• Can be repeated by anyone and get the same results.
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• Test only one variable.
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• Does not have to agree with the hypothesis.

Sample Problem
An experiment was carried out using ten plants of the same species. Growth hormones were added to the soil for the purpose of making the plants grow taller.

State the hypothesis.

• If you add growth hormones to plant soil, then the plants will grow taller.

How will the control group be treated different from the experimental group?

• The control group will not receive any hormones and the experimental group will.

Identify the independent variable.

• The growth hormones

Identify the dependent variable.

• Plant height

List two conditions that must be kept constant

• Same amount of water and same amount of sun

What can be done to make the result more meaningful?

• Use more plants
• Repeat the experiment
• Use different species of plants

What type of result would support your hypothesis?

• If the plants in the experimental group grow taller than the control group, my hypothesis is supported.

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INQUIRY 2 SCIENTIFIC METHOD

Designing a Controlled Experiment

When scientists want to find out why something happens the way it does, they conduct an experiment. Since they want the results of the experiment to be taken seriously by other scientists, they use a universal approach to solving problems called the scientific method.

The Scientific Method

Scientist generally follow three steps when they use the scientific method. First, they pose the question that they want to answer. Next, they form a hypothesis, their explanation or guess as to what the answer will be. Then they design and conduct an experiment that will either prove or disprove their hypothesis.
Step 1: Define the Problem

Begin by posing your question very carefully and specifically so you can carry out a proper investigation. If you do not have a good background of the problem, conduct a thorough research of all relevant information available to you, including books, journals, internet...
Step 2: Formulate a Hypothesis

Your hypothesis should be formulated in such a way that it answers the question that you are about to research. For example, if the question is "What is the effect of light intensity on plant growth?", then the hypothesis can be "If light intensity is increased, then plant growth will increase".

Step 3: Design and Conduct a Controlled Experiment

In order to find out whether your hypothesis is true or false, you must test it by conducting a controlled experiment. A controlled actually consist of two experiments run side by side. One is called the control group and the other is called the experimental group. The original experiment is called the control group. The second experiment duplicates the first, except for a single factor called the experimental variable, which you purposely change. If you make sure that only one factor differs between the two experiments, you can be confident that any difference in the results is due to this experimental variable.
Lets Practice Designing a Controlled Experiment

Suppose you want test the effect of light intensity on plant growth. You want to conduct a controlled experiment to find out whether your hypothesis is true or false, so you raise two sets of plants.

Write down anything else beside light intensity that influences plant growth and make sure that these factors remain the same in both groups of plants. For example, the amount of water, the type of soil, the amount of soil, the size of the pot, the temperature are factors that can contribute to plant growth. All these factors must be the same in both groups. The only thing that can be changed in the test group is the light intensity, which is also referred to as the independent variable.

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