Constant or Controlled Variables

8th Grade Science

What is a Constant Variable?

• A constant variable is also called a Controlled variable. (or Extraneous variable)

• It is the parts of the experiment that have to be kept the same so the experiment is a fair test of the IV.

List the MOST important ones.

• There can be several variables that need to be controlled or kept the same in the experiment.

• To save time and space, just focus on the 3 variables that would have THE MOST INFLUENCE on the outcome of the experiment.

Where do you find it?

• Listing constant variables requires you to use your prior knowledge about the subject.

Target Practice

• Think of the constant variables in #1 on your worksheet:

• Does how fast a rose bush grows depend on the amount of sunlight it receives?

MOST influential variable

• Eliminate the IV (sunlight)!!!

• Look for OTHER things BESIDES the Independent variable that would influence the outcome (DV) of the experiment.

• Use your PRIOR knowledge about what a plant needs to grow.

Think…What causes bacteria to thrive?

• #2 Do bacteria reproduce at a faster rate if the temperature is warmer?

Got Bacteria??List the Constant Variables:

•Amount of moisture

•Amount of light

•nutrients

Try #3 on Your own

• What are all of the variables you have listed?– Amount of food ─environment– Type of chicken ─nesting materials– Size of chicken– Age of chicken– Amount of water– Temperature

Try #3 on Your own

• What are the most important?– Amount of food– Type of chicken – Size of chicken --Temperature

--Age of chicken ─environment– Amount of water --nesting materials– Health of chicken