1 2 Next Controlled Experiments A controlled experiment is a method of testing a prediction or hypothesis in which a relationship between different variables is identified. In a controlled experiment, a scientist designs an investigation in which most of the conditions of the experiment are strictly controlled. This allows a scientist to determine the relationship that two specific variables have with one another. Constants The constants in an experiment are all the conditions that are kept exactly the same throughout the experiment. These conditions are kept the same so that a scientist can tell if or how one specific variable is changing another variable. For example, consider a situation in which a scientist is conducting an experiment with sunflowers. https://app107.studyisland.com/cfw/content/show lesson/b810b54a?cfid=e00ec46a e5df 4df7 911c ad2b2b62bfbf&cftoken=0&apprnd=1497022914455 1/5
If, for example, Dr. Smith is running an experiment to determine which plant food helps sunflowers grow the tallest, some of the things he will want to keep constant include: the size of the pot each sunflower is in the type of soil he uses in each pot the amount of water he gives each plant the amount of sunlight each plant gets the type of sunflower seeds he uses the number of sunflower seeds he plants in each pot All of the above are variables that Dr. Smith must control and keep constant if he wants his experiment to be successful. Independent & Dependent Variables The independent variable in an experiment is what is purposely changed by the scientist. In Dr. Smith's sunflower experiment, he wants to find out how the plant's height responds to a change in plant food. So, while everything else is held constant, Dr. Smith will be changing the type of plant food that he gives each sunflower. https://app107.studyisland.com/cfw/content/show lesson/b810b54a?cfid=e00ec46a e5df 4df7 911c ad2b2b62bfbf&cftoken=0&apprnd=1497022914455 2/5
The independent variable in Dr. Smith's experiment will be the plant food. He will give each pot of plants a different kind of plant food. The dependent variable is the factor in an experiment that is allowed to change on its own in response to the independent variable. Exactly how the dependent variable changes, or does not change, should be recorded and analyzed in order to make a conclusion about the results of the experiment. In Dr. Smith's case, his dependent variable is the height of each plant. It is dependent because it depends on which plant food (the independent variable) is given to the sunflower. https://app107.studyisland.com/cfw/content/show lesson/b810b54a?cfid=e00ec46a e5df 4df7 911c ad2b2b62bfbf&cftoken=0&apprnd=1497022914455 3/5
The dependent variable will change (or not change) as a result of the independent variable that is being manipulated by the scientist. Dr. Smith's dependent variable will be the height of each sunflower. Control Groups A control group represents the "normal" case, when the independent variable has not been tampered with. Control groups are used to give a "normal" result that a scientist can compare the experimental results to. In the case of Dr. Smith's experiment, the control group would include sunflowers that were given no plant food at all. By comparing the other sunflowers to his control group, Dr. Smith can tell exactly how big of a difference the plant food made. Common Experimental Mistakes There are numerous mistakes that could be made while running an experiment. These mistakes can lead to inaccurate or inconclusive results. https://app107.studyisland.com/cfw/content/show lesson/b810b54a?cfid=e00ec46a e5df 4df7 911c ad2b2b62bfbf&cftoken=0&apprnd=1497022914455 4/5
Sometimes, errors are made regarding the independent variable. If more than one variable is changed at the same time in an experiment, then the outcome of the experiment may not be attributable to any one of the variables. So, if Dr. Smith changed not only the type of plant food, but also the amount of water that he gave each sunflower, then it might be impossible to tell if the resulting plants' heights were due to the food or the water. Another common mistake is not properly identifying all of the constants. What if Dr. Smith forgot to make sure that he bought sunflower seeds that were all of the same type? What if Dr. Smith forgot to make sure that the same quality of soil was put in each pot? It is very important that these variables are identified and made exactly the same. Otherwise, the conclusions of the scientific investigation may not be valid. Comment on Lesson Copyright 2017 Edmentum All rights reserved. https://app107.studyisland.com/cfw/content/show lesson/b810b54a?cfid=e00ec46a e5df 4df7 911c ad2b2b62bfbf&cftoken=0&apprnd=1497022914455 5/5