Keys to Conducting a Good Experiment

 Variables- the things you change in an experiment

 Independent variable- the one factor you change in the

experiment 

Dependent variable- the factor that changes as a result of the experiment

 Constants- the factors that stay the same during the experiment

 Control group- the group you use as a comparison

   

IMPORTANT 

You only change one variable in an experiment, all other variables stay the same.

A HYPOTHESIS 

A statement about what you predict will happen in the experiment. A hypothesis is sometimes proven to be incorrect. A hypothesis is written as an “If”, “Then”

and “Because” statement.  

If, (Independent Variable) Then, (Dependent Variable) Because, (Scientific Explanation)

  

If a hypothesis is shown to be incorrect then it may be revised and tested again through continued

experimentation, or the rejection of the hypothesis could be considered to be the conclusion.

EXAMPLE EXPERIMENT 

You conduct an experiment to see how different amounts of water may affect plant growth.

You only change the amount of water you give the plants.

The amount of water is the Independent Variable.

The amount the plants grow is the Dependent Variable.

You use the same type of plants, the same type of soil, the same size pot, the same amount of light and keep them at

the same temperature. These are the Constants. 

The group of plants that receive the least amount of water will be the Control Group.

  

Sample HypothesisIF I give plants increased amounts of water THEN, they will

increase in growth proportionately BECAUSE, they need water to photosynthesize and grow.

EXPERIMENTAL DESIGN continued…

 When you design an experiment you need to have a

detailed and comprehensive list of the materials that will be needed and a procedure to follow.

 Materials and procedures are always written as

numerical lists. 

Winning projects tend to have at least 30 tests in order to perform thorough data analysis.

EXAMPLE EXPERIMENTAL DESIGN Materials:1-60 Wisconsin Fast Grow plants2-60 pots same size3-potting soil4-natural light or artificial light set up5-graduated cylinder6-metric ruler

EXAMPLE EXPERIMENTAL DESIGN…Procedure:1. Fill pots with potting soil until almost full.2. Put 1 seed in each pot at a depth of ½ pinkie.3. Divide plants evenly into 4 groups labeled: A, B, C, D.4. All plants should be kept at the same temperature and receive equal amounts of light daily.5. Group A should receive 10 mL of water. It is the Control Group.6. Group B should receive 20 mL of water.7. Group C should receive 30 mL of water.8. Group D should receive 40 mL of water.9. Re-water each group using these amounts 1X per week.10. Measure growth weekly and record data in your Project Journal.11. Take photographs weekly and include these in the Project Journal.