Variable Definitions Scientific Method

Variable Anything that can “vary” or change that might effect our data.

Independent Variable Variables The one and only variable that I change or manipulate. This is THE CAUSE. Also called the “manipulated variable” Dependent Variable This variable is “dependent” on and responds to the change in the I.V. This is the data we collect. This is THE EFFECT. Also called the “responding variable”

Variables Continued Controlled Variables (aka “controls”) These are all the other variables that might effect the outcome of our experiment. They must be controlled! We want them to be exactly the same in BOTH the Experimental Group and Control Group. Uncontrolled Variables Variables that should have been controlled but were overlooked (not controlled). If recognized, these should be discussed in the lab report.

Experimental Group Control Group The group on which you apply or change the independent variable. Control Group The “normal” group, used for comparison.

Example: Sugar Water Plants Problem: Mr. Frost was wondering if sugar would help plants grow faster. Background: Sugar is chemical energy. All living things need energy in order to grow and exist. Plants are living things, so perhaps they would benefit from sugar in the water. Hypothesis: If sugar is added to the water, then the plants will grow more quickly, because plants need energy to grow and they absorb water through their roots.

Example: Sugar Water Plants Think “Cause & Effect” = “I.V. & D.V.” Mr. Frost thinks the sugar will cause the plants to grow faster, so… I.V. = sugar in water or not D.V. = plant growth rate

Control Group Vs. Experimental Group The Experimental Group is the group in which we change and test the I.V. Example: The group of plants that I add sugar to. The Control Group is the “normal” group and is used for comparison. Example: The group that received regular water like normal.

Example: Sugar Water Plants Controlled Variables: Same type of seeds, planted same depth, same type and amount of soil, same type and amount of water (except experimental group gets sugar in the water), same size and type of pots, same temperature, same amount of light, same watering technique… can you think of others? Uncontrolled Variables: ?? Are there other variables that might affect the outcome of this experiment but which I have failed to control? If so, we need to note them. They are uncontrolled variables.