What Is an Experimental Constant

A constant is a quantity that does not change. Although you can measure a constant, you either cannot alter it during an experiment or else you choose not to change it. Contrast this with an experimental variable, which is the part of an  experiment that is affected by the experiment.  There are two main types of constants you may encounter in experiments: true constants and control constants. Here is an explanation of these constants, with examples. Physical Constants Physical constants are quantities which you cannot change. They may be calculated or defined. Examples: Avogadros number, pi, the speed of light, Plancks constant Control Constants Control constants or control variables are quantities a researcher holds steady during an experiment. Even though the value or state of a control constant may not change, it is important to record the constant so the experiment may be reproduced. Examples: temperature, day/night, duration of a test, pH