Control Groups in Science Projects
Most experiments are made up of a control group and an experimental group. The results from each group are measured and compared to one another. This allows the scientist to determine exactly what has caused any changes that occur during the experiment. Use of a control group is allows scientists to replicate and experiment, and to better understand the experiment's results.
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Control Groups Defined
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A control group is the part of the experiment in which you do not change the variable. The measurements you take from this group will give you a norm against which to measure the experiment. For instance, if you are conducting an experiment to see if salt makes water boil faster, you will want to heat one pan of water without salt and see how long it takes to boil. The unsalted water is your control group.
Experimental vs. Control Group
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The experimental group is the part of the experiment in which you change the variable. You will compare the results from the experimental group with the results of the control group to see what changing a single variable does. There must be only one variable changed between the control and experimental groups so that you are able to determine why the measurements changed or remained the same between groups. For the water experiment, the pan of water with salt is the experimental group. You must be sure that both pans have the same amount of water and are heated at the same temperature so that the only difference is the salt.
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Famous Experiment Using a Control Group
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In 1668 Francesco Redi disproved spontaneous generation by doing an experiment using a control and experimental group. At the time, people thought that aging meat generated maggots, but Redi suspected that flies laid eggs in the meat and when these eggs hatched, the maggots looked like they had spontaneously generated from the meat, even though they had not. In order to prove this, he used two pieces of meat. One, the control, was left out in the open as usual. The other, the experimental group, was covered in paper so that the flies could not reach it. The uncovered meat developed maggots while the meat covered in paper did not.
Examples of Experiments Using Control Groups
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If you want to see how much sunlight effects the growth of a plant, you can plant two seeds of the same plant in identical pots, placing one in the sunlight and one in the shade for your experimental and control groups. In a separate experiment, you could test a fertilizer to see if it made plants grow faster. Again, you would place two seeds in identical pots but this time you would put both pots in the same place so that they each got the same amount of light. Your control group would not get the fertilizer but your experimental group would.
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References
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