Identifying VariablesIdentifying Variables&&

Designing Designing InvestigationsInvestigations

3 Kinds of Variables3 Kinds of Variables

Independent Variable – something Independent Variable – something that is changed by the scientistthat is changed by the scientist What is testedWhat is tested What is manipulatedWhat is manipulated

3 Kinds of Variables3 Kinds of Variables

Dependent Variable – something that Dependent Variable – something that might be affected by the change in might be affected by the change in the independent variablethe independent variable What is observedWhat is observed What is measuredWhat is measured The data collected during the The data collected during the

investigationinvestigation

3 Kinds of Variables3 Kinds of Variables

Controlled Variable – a variable that Controlled Variable – a variable that is not changedis not changed Also called constantsAlso called constants Allow for a “fair test”Allow for a “fair test”

For Example:For Example:

Students of different ages Students of different ages were given the same jigsaw were given the same jigsaw

puzzle to put together. puzzle to put together. They were timed to see how They were timed to see how

long it took to finish the long it took to finish the puzzle.puzzle.

Identify the variables in Identify the variables in this investigation.this investigation.

What was the independent What was the independent variable?variable?

Ages of the studentsAges of the studentsDifferent ages were tested by Different ages were tested by

the scientistthe scientist

What was the dependent variable?What was the dependent variable?

The time it to put the puzzle The time it to put the puzzle togethertogetherThe time was observed and The time was observed and

measured by the scientistmeasured by the scientist

What was a controlled variable?What was a controlled variable?

Same puzzleSame puzzleAll of the participants were All of the participants were

tested with the same puzzle.tested with the same puzzle. It would not have been a fair It would not have been a fair

test if some had an easy 30 test if some had an easy 30 piece puzzle and some had a piece puzzle and some had a harder 500 piece puzzle.harder 500 piece puzzle.

Another example:Another example:

An investigation was done with an An investigation was done with an electromagnetic system made electromagnetic system made

from a battery and wire wrapped from a battery and wire wrapped around a nail. Different sizes of around a nail. Different sizes of nails were used. The number of nails were used. The number of

paper clips the electromagnet paper clips the electromagnet could pick up was measured.could pick up was measured.

What are the variables in this What are the variables in this investigation?investigation?

Independent variable:Independent variable:

Sizes of nailsSizes of nailsThese were changed by the These were changed by the

scientistscientist

Dependent variable:Dependent variable:

Number of paper clips picked Number of paper clips picked upupThe number of paper clips The number of paper clips

observed and counted observed and counted (measured) (measured)

Controlled variables:Controlled variables:

Battery, wire, type of nailBattery, wire, type of nail None of these items were changedNone of these items were changed

One more:One more:

The higher the The higher the temperature of water, temperature of water, the faster an egg will the faster an egg will

boil.boil.

Independent variable – temperature Independent variable – temperature of waterof water

Dependent variable – time to cook Dependent variable – time to cook an eggan egg

Controlled variable – type of eggControlled variable – type of egg

Last one:Last one:

The temperature of The temperature of water was measured at water was measured at

different depths of a different depths of a pond.pond.

Independent variable – depth of the Independent variable – depth of the waterwater

Dependent variable – temperatureDependent variable – temperature Controlled variable – thermometerControlled variable – thermometer

Designing InvestigationsDesigning Investigations

The greater the amount of soap in a The greater the amount of soap in a soap and water mixture, the bigger a soap and water mixture, the bigger a

soap bubble can be blown.soap bubble can be blown. Design an investigation to test this Design an investigation to test this

hypothesis.hypothesis. Identify the variablesIdentify the variables What exactly will be changed? How What exactly will be changed? How

will it be changed?will it be changed? What exactly will be measured? How What exactly will be measured? How

will it be measured?will it be measured?

The farther a ball drops, the higher The farther a ball drops, the higher it will bounce.it will bounce.

Design an investigation to test this Design an investigation to test this hypothesis.hypothesis. Identify the variablesIdentify the variables What exactly will be changed? What exactly will be changed?

How will it be changed?How will it be changed? What exactly will be measured? What exactly will be measured?

How will it be measured?How will it be measured?