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The Control Sets the Standard
By definition the control in a science experiment is a sample that remains the same throughout the experiment. The control must remain the same or equal at all times in order to receive accurate results. You can have as many controls as necessary to achieve results. For instance, when determining how far certain weights move based on wind velocity, the wind would be a control, staying the same, no matter what the weight.
Controls are a vital part of a science experiment. If at any point, your variable could affect the end result of your experiment, it should be considered the control. Your control may change as your experiment changes. For instance, you may need a different sample to prove a different hypothesis.
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How Does a Control Compare to Other Variables
When following the scientific method, you must have an independent and dependent variable. A control is just another type of variable. The three types of variables should not be confused as they are completely different.
Independent variables are changes occurring due to the person doing the experiment.
Dependent variables change based upon changes in the independent variables. Controlled variables are any other outside variables that may affect the dependent variable.
The three variables can sometimes be easily mistaken. If you have not identified the control in a science experiment, you may be mistaking one of your controls as an independent variable.
Remember that the control should never change. If your independent variable always remains the same, odds are it is your control.
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How to Create Your Own Control Sample
Now we've covered what is a control in a science experiment, it's time to see how it works in practice. Not all science experiments require a control, but many do. You can create your own control sample by following a few simple steps.
One great example of creating a control in a relatively simple experiment is working with plants. The basis is to determine how plants grow in different types of soil mixtures. The control pot uses regular potting soil and the same daily routine of water and sun.
The other pots have different soil mixtures and may be exposed to varying lights and temperatures.
Depending on your science experiment, determine a variable or sample set that must remain the same at all times. The control may directly apply to every portion of your experiment, or it can be relative, such as the plant experiment.
Another great example of creating a control is determining how fast an object sinks, or the object's density. The control would be using the same amount of water in the exact same size container. Be sure to use the same type of water as well, such as filtered or unfiltered.
Once the science experiment starts, document what your control is, along with your independent and dependent variables. This allows you to better monitor and keep track of your controlled variable. Controlled variables must be carefully set and monitored throughout your experiment. Any changes to the control will greatly alter your experiment's results.
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Science Fair Project - http://sciencefairproject.virtualave.net/scientific_method.htm
Cool Science Projects - http://www.cool-science-projects.com/independent-and-dependent-variables.html
Image Credits: Wikimedia Commons / Adrignola