# Explain how a variable differs from a constant

### October 26, 2019

How a variable differs from a constant

Constants

Experimental constants are values that do not change either during or between experiments. Many natural forces and properties, such as the speed of light and the atomic weight of gold, are experimental constants. In some cases, a property can be considered constant for the purposes of an experiment even though it technically could change under certain circumstances. The boiling point of water changes with altitude and acceleration due to gravity decreases with distance from the earth, but for experiments in one location, these can also be considered constants.
Constants, also known as controlled variables, are elements that are carefully monitored to ensure that they stay the same across all the experimental groups.

## Purpose

Having constants in a science fair project helps to ensure that any differences between experimental groups are an effect of the independent variable that is being studied, not other factors.

## Identification

Constants must be identified before the experiment is begun. A good way to identify constants is to ask the question of what else might affect the dependent variable, which is the element being measured in the science fair project.

## Example

For example, in a science fair project that is measuring the effect of room temperature on the growth of broccoli seedlings, room temperature is the independent variable and the height of seedling is the dependent variable. The constants include the type of pot, type and amount of soil, watering schedule and the depth at which seeds are planted.
Sometimes certain characteristics of the objects under scrutiny are deliberately left unchanged. These are known as constant or controlled variables. In the ice cube experiment, one constant or controllable variable could be the size and shape of the cube. By keeping the ice cubes' sizes and shapes the same, it's easier to measure the differences between the cubes as they melt after shifting their positions, as they all started out as the same size.

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