Identifying Variables & the Control Group

3 Kinds of Variables Independent Variable (IV) Dependent Variable (DV) Controlled Variables (CV)

Independent Variable The independent variable is something that is changed by the scientist What is tested What is manipulated (changed)

Dependent Variable The dependent variable is something that might be affected by the change in the independent variable What is observed What is measured The data collected during the investigation

Controlled Variables The controlled variables (constants) are variables that are not changed Are kept the same for every test Allow for a “fair test”

For Example:

Do together as a class: 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.

What was the independent variable? Ages of the students Different ages were tested by the scientist

What was the dependent variable? The time it to put the puzzle together The time was observed and measured by the scientist

What was a controlled variable? 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:

fully melts she records the time. Work in table groups: Bailey wants to find which frozen liquid melts fastest: soda, orange juice, or water. She pours each liquid into an empty ice cube tray. After 8 hours she takes them out and place one cube of each on its own plate. When each fully melts she records the time.

What are the variables in this investigation? Independent Variable (IV)? Dependent Variable (DV)? Controlled Variable (CV)?

Independent variable: Type of liquid These were changed by the scientist

Dependent variable: Time How long did it take to melt?

Controlled variables: (constants) Amount of liquid, freezing time, type of plate None of these items were changed

Control Groups

A control group in a scientific experiment is a group where the factor being tested is NOT applied so that it may serve as a standard for comparison against another group where the factor IS applied.

You water three sunflower plants with salt water You water three sunflower plants with salt water. Each plant receives a different concentration of salt solutions. A fourth plant receives pure water. After a two week period, the height is measured.

What is the control group? The pure water plants

One tank of gold fish is fed the normal amount of food once a day, a second tank is fed twice a day, and a third tank four times a day during a six week study. The fish’s weight is recorded daily.

What is the control group? Normal food group

What is the importance of a control group? Serves as a basis for comparison

Let’s try a challenge…..

The time it takes to run a mile depends on the person’s running speed. What are the… IV? DV? CV? Running speed Time to run mile Person, location, weather, clothing, etc.

A student wanted to test how the mass of a paper airplane affected the distance it would fly. Paper clips were added before each test flight. As each paper clip was added, the plane was tested to determine how far it would fly. What is the control group? A plane with no paper clips

Worksheet will now be given and is due tomorrow.