As scientists continue to figure out how nature works, they do so by use of experiments, with an aim of searching for cause and effect relationships. These relationships are used to explain why things happen and allow one to predict what will happen if a certain event occurs. The role of these experiments hence is to observe and measure how changes occur in relation to other things. In an experiment, the things that change are referred to as variables. 

What is a Constant?

These are values that do not change during experiments. 

For example, in an experiment where one wants to test how the growth of plants is affected by the amount of water, factors like type of soil, temperature, type of plant and sunlight all stay the same in the course of the experiment. These are hence referred to as the constants in this experiment, while the amount of water is the control.   

Other examples include freezing and boiling points of water, the speed of light, 

What is Controls?

A controlled variable is a variable that could change but is intentionally kept constant in order to clearly show the relationship between dependent and independent variables. It is also a variable that is not of primary interest and hence constitutes a third factor whose influence is to be controlled or eliminated. These variables either need to be kept constant during the experiment or be monitored and recorded. This ensures that their influence can be assessed. Most experiments have more than one control. 

An example used to explain control variable is the effect of fertilizers on a plants growth, whereby the growth of plants differs based on the amount of fertilizer used. The fertilizer, in this case, is the control variable. 

Other examples include time, pressure and temperature.

Similarities between Constant Vs. Control

• Both are important in experiments as they determine the outcome

Differences between Constant and Control

1. Variation

A constant variable does not change. A control variable on the other hand changes, but is intentionally kept constant throughout the experiment so as to show the relationship between dependent and independent variables.  

2. Primary interest

While the constant is the variable of primary interest, the control is not; hence its influence can be controlled or eliminated. 

Constant vs. Control: Comparison Table

Summary of Constant vs. Control

In an experiment, both constant and control variables are important as they influence the outcomes of the experiments. 

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