Aim: What are variables in science experiments?

Focus: What makes an experiment “fair”?

Variables

A variable is something that is changed

A constant, or control, is something that does not change

Aim: What are variables in science experiments?

Science experiments use…

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

Aim: What are variables in science experiments?

A birdy example…

Imagine you want to see what color of bird feeders your local birds preferred.

Red? Blue? Green?

Aim: What are variables in science experiments?

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

Aim: What are variables in science experiments?

Our Experimental DesignConstants Location of feeders

Kind of seed

Type of feeder

Independent

Variable Red Blue Green

Dependent

Variable

Amount of Seed Eaten

Amount of Seed Eaten

Amount of Seed Eaten

Aim: What are variables in science experiments?

If everything except the independent variable is held

constant, we can say:

The experiment is FAIR.

(ONLY the independent variable can change!)

Aim: What are variables in science experiments?

Why is it important to only change the independent variable?

Aim: What are variables in science experiments?

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.

Independent Variable

Aim: What are variables in science experiments?

Aim: What are variables in science experiments?

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!

Aim: What are variables in science experiments?

Is Jessie’s experiment fair?

NO! It isn’t fair since the feeders are not out at the same time, and we know that the weather is very different each day. Perhaps the number and kind of birds that visited during the week were different due to the different weather.

Saturday (Snowy)

Tuesday(Sunny)

Monday (Rainy)

Aim: What are variables in science experiments?

What do you think?Terry loves birds and wants to see as many as she

can in her yard. She wants to know whether she is wasting money buying an expensive mixed seed, when a cheaper brand just arrived at her local store. She wonders… will the expensive seed attract more birds to her back yard?

How would you advise her to find out if the expensive seed is better?

Aim: What are variables in science experiments?

Terry’s Experimental Design

Independent

Variable ?

Dependent

Variable ?

Constants ?

Aim: What are variables in science experiments?

Terry’s Experimental DesignIndependent

Variable

Kind of seed:

Expensive Cheap

Dependent

Variable

Number (and perhaps kinds) of birds that visit

Constants Location of feedersType of feederWay she measures the amount of seed eaten and the way she counts birds

$

Aim: What are variables in science experiments?