How to Design an Experiment

Transcription

1 Introduction In this activity, you will review how to design an experiment by identifying the independent variable, dependent variable and control. These are skills you will use throughout the year, if not throughout your career in science classes at the Upper School. Pay careful attention and do your best. Your picture here

2 The Independent Variable The independent variable in an experiment is the variable that is controlled by the researcher. For instance, in a study on the effect of fertilizer on tomato plants, the independent variable would be the fertilizer. This is the variable the researcher changed on purpose. Take the following quiz to see if you can identify the independent variable: Quiz on Finding the Independent Variable. Quiz!QuiU The Dependent Variable The dependent variable in an experiment is the variable that is measured by the researcher. For instance, in the previously mentioned study on the effect of fertilizer on tomato plants, ask yourself, How will the experimenter know if the fertilizer made a difference? The dependent variable should be measurable in this case, you could measure the height of the plant or the weight of the tomatoes. Take the following quiz to see if you can identify the dependent variable: Quiz on Finding the Dependent Variable. HU 2

3 The Control The control is the standard for comparison in an experiment. It is not affected by a change in the independent variable. In the example we ve been using, a group of tomato plants (at least three in each experimental group are needed!) will receive all the same conditions as the other plants but they will not receive the independent variable which is the fertilizer, in this experiment. That way, the experimenter will know that if the group of plants that received the fertilizer grow larger (or produce larger tomatoes) than the control group, it must be due to the fertilizer (since that s the only difference between the two groups). Take the following quiz to see if you can identify the control: Quiz on Finding the Control. HU The Hypothesis A hypothesis should be written as an, If, then statement. Following the If is the independent variable, and the dependent variable follows the then. For instance, you might state, If I apply fertilizer to tomato plants, then they will get taller (or produce larger tomatoes). You may even want to specify in your hypothesis that the tomato plants receiving the most fertilizer will grow the tallest (or produce the largest tomatoes). Take the following quiz to see if you can identify the control: Quiz on Creating the Hypothesis.

4 Constants When conducting an experiment, it is important that your experimental groups receive all the same conditions except for the purposeful change you ve made in the independent variable. This is the reason for constants. In our tomato plant experiment, where our independent variable is whether or not plants receive fertilizer (or we could choose to change the amount of fertilizer they get), our constants will be all the other conditions our tomato plants are subject to. This would include soil (type and amount), water (type and amount), size and type of pot plants are in, tomato plants used in experiment (type, sizes, age), amount of sunlight plants receive, etc. This list could go on for some time, becoming more and more specific. With your constants, please try to include the most important ones (for instance, when thinking of growth the amount of sunlight and water plants receive better be included as constants!) and include a minimum of three but feel free to list more! You need to keep these constant when you do the experiment! Take the following quiz to see if you can identify the appropriate constants: Quiz on Listing Important Constants

5 References Cothron, Julia H., Ronald N. Giese, and Richard J. Rezba. Science Experiments and Projects for Students. Dubuque, Iowa: Kendall/Hunt, Holsinger, Rachel and Debbie Wheeler. Lab 2: How to Design an Experiment. Sayre School: Lexington, KY. August 2006.