IDENTIFYING VARIABLES

Variable Change Able to Variable: A factor that can change in an experiment. Every experiment has two – one is the cause, the other is the effect.

Cause and Effect Does crushing a sugar cube effect the rate at which the sugar dissolves in the water? What is the cause and what is the effect?

Crushing the sugar cube will effect how long it takes to dissolve. Crushing the sugar cube is what we predict will be the cause. This is called the Independent Variable. Crushing the sugar cube will effect how long it takes to dissolve. This is called the Dependent Variable. The time it takes to dissolve is what we will see the effect on.

Independent variable The variable or one factor that is being changed in the experiment (‘I choose’)

Dependent variable The variable that is being measured in the experiment or what we predict will be affected. (‘Depends on what I choose’)

Age Chances of divorce fertilizer Plant height weather behavior IV- DV- Experiment Title: Does the age of a person gets married effect their chances of getting a divorce? Experiment Title: Does fertilizer affect plant height? Experiment Title: Is there are relationship between the weather and how students behave? IV- DV- fertilizer Plant height IV- DV- weather behavior

Check for Understanding Does brushing your hair make it grow faster? Identify the independent variable.  Ask yourself: what is the cause? Identify the dependent variable Ask yourself: what is the effect?

Check for Understanding Do car accidents increase your car insurance cost? Identify the independent variable. Identify the dependent variable.

All factors that stay the SAME in the experiment so we can determine only one factor is causing the effect. CONSTANT

Practice with Constants Does fertilizer affect plant height? Independent Variable: fertilizer Dependent Variable: plant height How can we be sure that the fertilizer is the ONLY THING affecting the plant height? We must have a control to make sure that the fertilizer is the only factor affecting plant height. We must use THE SAME type of plant, let the plants get the SAME amount of sunlight Constants: type of plant, amount of sunlight

Practice with Constants Does the temperature outside effect the chances a person will get the flu? -IV: Temperature outside -DV: Chances a person will get the flu Whether or not someone gets the flu could depend on the person, so in order to determine if the temperature is the reason, we must use the SAME person -Constant: Person

Check for Understanding What effect does a car’s speed have on gas mileage? Identify the constant. Constant = The car used, the distance driven

Check for Understanding Does adding salt to water affect the temperature at which it boils? Identify the constant. Constant = The source of the water (where the water came from), the amount of water used, the size of the pot

A birdy example… Imagine you want to see what color of bird feeders your local birds preferred. Red? Blue? Green? If a student wanted to determine whether feeder color has an effect, he might suggest, “if I put up a red, blue, and green feeder, birds will visit the green feeder more” as a hypothesis. He might speculate that the green feeder, being the most “camouflaged” or “natural” might be visited the most.

Our Constants and Variables Independent Variable: color of the feeders Dependent Variable: amount of seed eaten Constants: everything else that is kept the same, for example: the location of the feeders the kind of feeder used putting the feeders out at the same time Independent Variable: the one factor that is changed by the person doing the experiment Dependent Variable: the factor which is measured in the experiment Constants: all the factors that stay the same in an experiment

Our Experimental Design Constants Location of feeders Kind of seed Type of feeder Independent Variable Red Blue Green Dependent Amount of Seed Eaten

The experiment is FAIR. (ONLY the independent variable can change!) If everything except the independent variable is held constant, we can say: The experiment is FAIR. (ONLY the independent variable can change!)

Why is it important to only change the independent variable? Collect answers…

If you don’t… If you measure a change in the dependent variable, you won’t know whether it is the independent variable that is causing the change. Give an example: a girl wanted to know whether her dog being out in the backyard scared birds away. She thought it would, because the dog likes to bark a lot and has been known to chase little animals. For 5 days when the dog was out, she counted for an hour. For 5 days the dog wasn’t out, she counted for an hour. After she collected the data, she noticed that birds are actually out MORE when the dog is in the yard. Does that surprise you? But, what the girl didn’t think of was other things that might effect the number of birds that were out. She began thinking that maybe something else might be going on. She realized that the dog was out on sunny warm days, and not on rainy, cool days. So, even though she found a change, how will she know if it was the dog may have had an effect? Or was it the weather? See if kids can suggest improvements to the experiment. (i.e. making sure the weather and temperature is similar on the days she counts.) Independent Variable

Is Sam’s experiment fair? YES? NO? Read the following scenario to the students: Sam wants to know if birds prefer one color of feeder to another. He makes three feeders out of 2-liter bottles and paints one red, one blue, and one green. He fills the feeders with the same amount of sunflower seed, and plans to keep the feeders out for one week before measuring how much seed is eaten out of each. On Tuesday, he puts each of the feeders in his back yard: the red feeder in a large dead tree, the blue feeder he sits on the doghouse, and the green one he puts in a small bushy tree. Is Sam’s experiment fair? NO! It isn’t fair since the locations of the feeders were very different!

Is Maria’s experiment fair? YES? NO? YES! It seems fair since Maria only changed the feeder color! Read the following scenario to the students: Maria wants to know if birds prefer one color of feeder to another. She makes three feeders out of 2-liter bottles and paints one red, one blue, and one green. She fills each of the feeders with the same amount of mixed birdseed, and plans to keep the feeders out for 10 days before measuring how much seed is eaten from each feeder. She puts each of the feeders in the school courtyard in a small tree, hanging each at the same height. Does Maria’s experiment seem fair?