# Identifying Variables & Designing Investigations.

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Identifying Variables & Designing Investigations

GOBSTOPPER VARIABLES  SIZE (BIGGER/SMALLER)  CRUSHED  SHAPE  COLOR  BRAND  TEMPERATURE  QUANTITY

WATER  TYPE (SPRING, TAP)  TEMPERATURE  AMOUNT  CARBONATED  ADDING ANOTHER CHEMICAL LIKE AN ACID OR SOAP

CONTAINER  SIZE  SHAPE  TYPE OF BOTTOM  DIFFERENT MATERIAL (SYROFOAM WOULD INSLUATE AND IT WOULD TAKE LONGER)  DEPTH

3 Kinds of Variables  Dependent Variable –What is being tested  Time it takes for a gobstopper to dissolve.

3 Kinds of Variables  Independent Variable –what is being CHANGED.  Example: The liquid

3 Kinds of Variables  Controlled Variable – a variable that is not changed  Also called constants  Controlled variables stay the same in the investigation

For Example:

Students of different ages were given the same jigsaw puzzle to put together. They were timed to see how long it took to finish the puzzle.

Identify the variables in this investigation. Re-write as: ________ depends on ____________.

What was the independent variable?  The times it takes to complete the puzzle depends on the age of the students.  Ages of the students (INDEPENDENT VARIABLE)

What was the dependent variable?  The time it to put the puzzle together The time it takes to finish the puzzle DEPENDS on the age of the students. The time it takes to finish the puzzle DEPENDS on the age of the students.

What would be the controlled variable in this example?

 Same puzzle  All of the participants were tested with the same puzzle.  It would not have been a fair test if some had an easy 30 piece puzzle and some had a harder 500 piece puzzle.

Another example:

The number of puppies in a litter is determined by the size of the mother.

What are the variables in this investigation? The number of puppies in a litter depends on the size of the mother.

Independent variable:  Size of the mother – what could be changed

Dependent variable:  Number of puppies  The number of puppies DEPENDS on the size of the mother.

Controlled variables:  Type of puppies  None of these items were changed

One more:

The higher the temperature of water, the faster an egg will boil. The time it takes the egg to boil depends on the temperature of the water

 Dependent variable – time to cook an egg  Independent variable – temperature of water  Controlled variable – type of egg

Last one:

The temperature of water was measured at different depths of a pond.

 Dependent variable – temperature  Independent variable – depth of the water  Controlled variable – thermometer

Designing Investigations

The greater the amount of soap in a soap and water mixture, the bigger a soap bubble can be blown.  Design an investigation to test this hypothesis.  Identify the variables  What exactly will be changed? How will it be changed?  What exactly will be measured? How will it be measured?

The farther a ball drops, the higher it will bounce.  Design an investigation to test this hypothesis.  Identify the variables  What exactly will be changed? How will it be changed?  What exactly will be measured? How will it be measured?