VARIABLE |ˈVE(Ə)RĒƏBƏL|

ADJECTIVEADJECTIVE• NOT CONSISTENT OR HAVING A FIXED PATTERN;

LIABLE TO CHANGE. • ABLE TO BE CHANGED OR ADAPTED : THE DRILL HAS

VARIABLE SPEED.

NOUNNOUN• AN ELEMENT, FEATURE, OR FACTOR THAT IS LIABLE

TO VARY OR CHANGE.

VariablesVariables1

Keeping Things Fair

It is important for an experiment to be a fair testfair test.

To insure an experiment is a fair test, you must change only one factor at a time one factor at a time while keeping all other conditions the samesame.

Scientists use an experiment to search for cause cause and effectand effect relationships in nature.

Experiments are designed so changes to one item cause something else to vary in a predictablepredictable way.

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Variables

These changing quantities are called variables.

A variable is any FactorTrait orCondition

existing in differing amounts or types.

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Variables

An experiment usually has three kinds of variables:

1.1. IndependentIndependent

2.2. DependentDependent

3.3. ControlledControlled

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Independent Variable

Is one variable changed by a scientistscientist.

To insure a fair test, a good experiment has only one only one independent variable.

As the scientist changes the independent variable, he or she observesobserves what happens.

There should be only one only one independent variable for any valid experiment.

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Dependent Variable

The scientist focuses his or her observations on the dependent variable to see how it how it responds responds to the change made to the independent variable.

The new value new value of the dependent variable is caused by and depends on the value of the independent variable.

There can be more than one more than one dependent variable.

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Controlled Variables

Experiments also have controlledcontrolled variables.

Controlled variables are quantities remainingremaining constant

They must be observedobserved as carefully as the dependent variables.

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Variables are measured

In a good experiment, the scientist must be able to measure measure the values for each variable.

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More to Think About

The independent variable is the variable that is varied or manipulatedmanipulated by the researcher

The dependent variable is the responseresponse that is measuredmeasured.

An independent variable is the presumed causepresumed cause, whereas the dependent variable is the presumed presumed effecteffect.

The dependent variable provides the datadata you collect.

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Types of Variables

Remember these guides:Question Independent

VariableDependent Variables

Controlled Variables

What I change What I observe What I keep the same

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Types of Variables

Question Independent Variable

Dependent Variables

Controlled Variables

What I change What I observe What I keep the same

How much water flows through a faucet at different openings?

Water faucet opening (closed, half open, fully open)

Amount of water flowing measured in liters per minute

• The Faucet•Water pressure, or

how much the water is "pushing"

"Different water pressure might also cause different amounts of water to flow and different faucets may behave differently, so to insure a fair test I want to keep the water pressure and the faucet the same for each faucet opening that I test.”

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Types of Variables

Question

Independent Variable

Dependent Variables

Controlled Variables

What I change What I observe What I keep the same

Does fertilizer make a plant grow bigger?

Amount of fertilizer measured in grams.

•Growth of the plant measured by its height.

•Growth of the plant measured by the number of leaves.

•See Measuring Plant Growth for more ways to measure plant growth .

•Same size pot for each plant.•Same type of plant in each

pot.•Same type and amount of

soil in each pot.•Same amount of water and

light.•Make measurements of

growth for each plant at the same time.

"The many variables above can each change how fast a plant grows, so to insure a fair test of the fertilizer, each of them must be kept the same for every pot."

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Outcomes & Results

The outcome describes the resultsresults of your experiment.

Henry and Eliza conducted an experiment using plant fertilizer.They added different amounts of fertilizer to seven pots of beansprouts. The pots were the same size and had the same typeand amount of soil. They were given the same amount of seeds,light, and water. To find out how the fertilizer affected thegrowth of the sprouts, Henry and Eliza calculated the averageheight of the bean sprouts in each pot. Here are the factors intheir experiment:

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Outcomes & Results

Changed variable: ??Controlled factors:

1.1. ??

2.2. ??

3.3. ??

4.4. ??

5.5. ??Outcome: ??

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Outcomes & Results

Changed variable: amount of fertilizeramount of fertilizerControlled factors:

1.1. size of potssize of pots

2.2. amount of lightamount of light

3.3. amount of wateramount of water

4.4. amount of soilamount of soil

5.5. number of seedsnumber of seedsOutcome: average height of bean sproutsaverage height of bean sprouts

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