Questions to THINK about (You do NOT need to write these down!) What does it mean for something to vary? What does the word dependent mean? Imagine you are creating an experiment to test your hypothesis that tomatoes grow better with fertilizer. What are some steps you would take?

NOTES: Independent, Dependent, & Control/Constant Variables

As we know, the steps of the scientific method are… Make observations Choose a question or problem. Research using your 5 senses. Develop a hypothesis Write your procedures Experiment to test your hypothesis and collect results. Organize and analyze your data to make conclusions Evaluate experiment

Today, we are going to talk about the 3 main parts of a good experiment… Hint: It’s not blowing up our classroom!

Think about this… Let’s say that Brad has a pimple. He wonders what will get rid of it. He’s heard that putting toothpaste on the zit will get rid of it. He’s also heard that lemon juice will get rid of it. He decides to rub his face with lemon juice and toothpaste. The next morning his pimple is gone. But which thing cured him? The toothpaste or the lemon juice?

The Answer? How many of you think it was the toothpaste? Raise your hand. How many of you think it was the lemon juice? Raise your hand. The truth is…. THERE IS NO WAY FOR YOU TO KNOW FOR SURE BECAUSE THIS IS A BAD EXPERIMENT!!!

Every Good Experiment Has Three Things! Independent variable Dependent variable Control/Constant Variable(s) So What Are These?

Definitions Variable: anything in an experiment that can change.

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 affect the rate at which the sugar dissolves in the water? What is the cause and what is the effect?

This is called the independent variable Crushing the sugar cube is what we predict will be the cause. This is called the independent variable This is called the dependent variable The time it takes to dissolve is what we will see the effect on.

Definitions Independent variable: what you manipulate (cause to change) in an experiment

Independent Variables What you actually manipulate (change) to test your hypothesis There should only be ONE in an experiment Always on the X-axis of a graph

Definitions Dependent variable: what happens in an experiment because of the independent variable.

Dependent Variables Happens because of your independent variable It’s how you determine if your hypothesis was true or not Always on the Y-axis of a graph

Definitions Control/Constant Variables: what you keep the same. So it doesn’t interfere with your independent variable! A good experiment attempts to keep as many variables as constant as possible.

Definitions Control Group: any part of your experiment that you DO NOT add the independent variable to, so that it can be used for comparison. In other words, things that you keep the same throughout your experiment. In an experiment, you should always have something that you don’t change so that you can compare what you do change!

Definition Experimental Group(s): any part of your experiment that receives the independent variables being tested The experimental group is compared with the control group.

Example Larry was told that a certain muscle cream was the newest best thing on the market and claims to double a person’s muscle power when used as part of a muscle-building workout. Interested in this product, he buys the special muscle cream and recruits Patrick and SpongeBob to help him with an experiment. Larry develops a special marshmallow weight- lifting program for Patrick and SpongeBob. He meets with them once every day for a period of 2 weeks and keeps track of their results by recording how many marshmallows they can lift. Before each session Patrick’s arms and back are lathered in the muscle cream, while Sponge Bob’s arms and back are lathered with the regular lotion.

What is the Independent Variable? Larry is wondering how different lotions will affect how much Spongebob and Patrick can lift. He changes (manipulates) the type of lotion that each person gets. Therefore, the independent variable in this example is the TYPE OF LOTION he puts on each.

What is the dependent variable in this experiment? Since Larry is looking to see if the cream has an effect on how much someone can lift, the dependent variable is THE NUMBER OF MARSHMALLOWS THAT CAN BE LIFTED by Spongebob and Patrick The number of marshmallows each one can lift depends on the type of lotion they got (independent variable)

What were some variables that Larry kept constant? Or do consistently? Larry applied the lotion on both Spongebob and Patrick every day for 2 weeks. He gave them the same workout to test the effect of his independent variable. He rubbed the lotion on the same areas (back and legs) for both Patrick and Spongebob.

How else could have Larry “controlled” his experiment? Same amount of lotion? Used the same marshmallows for Spongebob and Patrick?

What is the Control Group (s)? In this experiment, what did Larry use to compare the muscle cream (the type of lotion that he changed) to? He used a regular type of lotion, one without any special properties, on Sponge Bob to compare his results. Larry could have also not put any cream on Sponge Bob to see if the cream that he put on Patrick differed.

What were the variables in our Heart Rate Inquiry Lab? Independent Variable: Some kind of exercise Dependent Variable: Heart Rate (Beats per minute) Control/Constant Variables:

What are the variables for the crushed sugar experiment? Independent Variable: Crushed or non-crushed sugar Dependent Variable: Time it takes for sugar to dissolve in minutes Control/Constant Variables:

Check for Understanding Ms. McGuirk wants to see which liquid will dissolve a metal nail. She read that acids have special properties to dissolve certain materials. She changed the different liquids to place her nails in. She then saw how many days it took each liquid to dissolve the nails. She also placed a nail in water so that she could compare how fast the other liquids dissolved the nail. Identify the independent variable. Identify the dependent variable. Identify the control group. Identify the experimental group. Identify at least 3 variables that you would control

Check for Understanding Tiara wanted to see which color Gatorade gave the step team the most energy for their upcoming competition. She changed the different flavors of Gatorade to give to each member. She then saw how many jumping jacks they could do during the beginning of their step practice. She gave one team member water to compare her results to. Identify the independent variable. Identify the dependent variable. Identify the control group. Identify the experimental group.