Variable (mathematics).

Variable (mathematics). Variable (mathematics), mathematical or physical quantity that does not have a fixed numerical value. A quantity that does have a fixed numerical value is known as a constant. Equations relate variables to each other by means of constants. For example, the equation d = ygt2 governs the distance d that a falling object travels in a given amount of time t. In this equation, d and t are variables while y and g (the acceleration due to Earth's gravity) are constants. (Although g does in fact vary slightly from place to place on Earth's surface, it is a constant for one particular set of observations made in one place.) The whole reason for writing the equation is to understand how the varying time affects the distance the object falls. Some constants do not change under any circumstances, for example pi (p), which always has the value 3.14159265... and is therefore known as a universal constant. There are two types of variables in a scientific experiment: dependent and independent. The dependent variable is the variable being measured, while the independent variable can be controlled by the experiment. In understanding the relationship between the distance an object falls and the time it takes to fall that distance, one possible experiment would be to measure the different distances the object had fallen after different chosen times. The dependent variable in this case would be the distance fallen, d , and the independent variable would be the time, t, because the distance fallen depends on the elapsed time. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.