Identifying VariablesIdentifying Variables

Kinds of VariablesKinds of Variables

Independent Variable Independent Variable – something – something that is changed by the scientistthat is changed by the scientist What is testedWhat is tested What is manipulatedWhat is manipulated Changed on purpose to see what may Changed on purpose to see what may

happenhappen

Kinds of VariablesKinds of Variables

Dependent Variable Dependent Variable – something that – 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

Kinds of VariablesKinds of Variables

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

The Bread ExperimentThe Bread Experiment

LetLet’’s discuss variables, constants and s discuss variables, constants and controls using the bread experiment!controls using the bread experiment!

Problem/QuestionProblem/Question

John watches his John watches his grandmother bake grandmother bake bread. He asks his bread. He asks his grandmother what grandmother what

makes the bread rise.makes the bread rise.

She explains that yeast She explains that yeast releases a gas as it releases a gas as it

feeds on sugar.feeds on sugar.

Problem/QuestionProblem/Question

John wonders if the John wonders if the amount of sugar used amount of sugar used in the recipe will affect in the recipe will affect the size of the bread the size of the bread

loaf?loaf?

HypothesisHypothesis

The hypothesis is an educated The hypothesis is an educated guess about the relationship guess about the relationship

between the independent and between the independent and dependent variables.dependent variables.

Note: These variables will be Note: These variables will be defined in the next few slides.defined in the next few slides.

Do you know the difference Do you know the difference between the independent and between the independent and

dependent variables?dependent variables?

Independent VariableIndependent Variable The independent, or The independent, or

manipulated variable, is a factor manipulated variable, is a factor thatthat’’s intentionally varied by the s intentionally varied by the

experimenter.experimenter.John is going to use 25g., 50g., John is going to use 25g., 50g.,

100g., 250g., 500g. of sugar in 100g., 250g., 500g. of sugar in his experiment.his experiment.

Dependent VariableDependent Variable The dependent, or responding The dependent, or responding variable, is the factor that may variable, is the factor that may change as a result of changes change as a result of changes

made in the independent made in the independent variable.variable.

In this case, it would be the size In this case, it would be the size of the loaf of bread.of the loaf of bread.

Control GroupControl Group

In a scientific experiment, the In a scientific experiment, the control is the group that serves control is the group that serves as the standard of comparison.as the standard of comparison.

The control group may be a The control group may be a ““no no treatment" or an treatment" or an ““experimenter experimenter

selectedselected”” group. group.

Control GroupControl Group

The control group is exposed to The control group is exposed to the same conditions as the the same conditions as the

experimental group, except for experimental group, except for the variable being tested.the variable being tested.

AllAll experiments should have a experiments should have a control group.control group.

Control GroupControl Group

Because his grandmother Because his grandmother always used 50g. of sugar in always used 50g. of sugar in

her recipe, John is going to use her recipe, John is going to use that amount in his control that amount in his control

group.group.

ConstantsConstants

John has to keep all John has to keep all other factors the same other factors the same so that any observed so that any observed changes in the bread changes in the bread can be attributed to can be attributed to the variation in the the variation in the amount of sugar.amount of sugar.

ConstantsConstants

The constants in an The constants in an experiment are all the experiment are all the

factors that the factors that the experimenter attempts experimenter attempts

to keep the same. to keep the same.

Can you think of some Can you think of some constants for this constants for this

experiment?experiment?

ConstantsConstantsThey might include:They might include:

Other ingredients to the Other ingredients to the bread recipe, oven used, bread recipe, oven used,

rise time, brand of rise time, brand of ingredients, cooking time, ingredients, cooking time,

type of pan used, air type of pan used, air temperature and humidity temperature and humidity

where the bread was where the bread was rising, oven temperature, rising, oven temperature,

age of the yeast… age of the yeast…

Another Example:Another 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.

Yet Another example:Yet Another example:

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

Guess what?Guess what?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 egg and Controlled variable – type of egg and amount of wateramount of water

Last one:Last one:(I promise)(I promise)

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 – thermometer Controlled variable – thermometer

and pondand pond

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?

VariablesVariables

Independent Independent Variable- soapVariable- soap

Dependent Dependent Variable- size of Variable- size of bubble blownbubble blown

Controlled Controlled Variable-water and Variable-water and type of soaptype of soap

Amount of soap in Amount of soap in water mixturewater mixture

Size of the bubble Size of the bubble blown with different blown with different amounts of soap in amounts of soap in the waterthe water

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?

VariablesVariables

Independent Independent Variable- length of Variable- length of fallfall

Dependent Variable-Dependent Variable-height of bounceheight of bounce

Controlled Variable- Controlled Variable- ball, surface, size of ball, surface, size of the ballthe ball

The length of the fall, The length of the fall, different fall for each different fall for each trialtrial

The height of the The height of the bounce from the bounce from the different lengths of different lengths of the fall ~ the higher the fall ~ the higher the height of the fall the height of the fall the higher the the higher the bouncebounce