Controls and Variables

As we know, the steps of the scientific method are… Choose a question or problem. Research using your textbook, internet or your observations. Develop a hypothesis. Write your procedures Experiment to test your hypothesis. Organize your data. State your conclusion.

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 So What Are These?

Definitions Variable: anything in an experiment that can change.

Variable Change Able to Variable: Something 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.

Definitions Variable: anything in an experiment that can change Independent variable (I.V.): what you manipulate (or cause to change) in an experiment INDEPENDENT VARIABLE = think “CHANGE”

Independent Variables What you actually manipulate to test your hypothesis There should only be ONE in an experiment

Learning Through An 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 gets 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. Before each session Patrick’s arms and back are covered in the muscle cream, while Sponge Bob’s arms and back are covered 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 LOTION he puts on each.

Definition 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 supported or not It “depends” on the change. DEPENDENT VARIABLE – think “measure” because it is the thing that you will measure to see if your prediction (hypothesis) was right.

Learning Through An 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 gets 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. Before each session Patrick’s arms and back are covered in the muscle cream, while Sponge Bob’s arms and back are covered with the regular lotion.

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)

Definition Control: what you keep the same. So it doesn’t interfere with your independent variable! (You use this in an experiment to compare to what you do change.)

Control The control is used to compare! In an experiment, you should always have something that you don’t change so that you can compare what you do change! When Stephanie conducted her experiment, she told half of the class not do their homework, while the other half of the class remained the same (they did their homework) Then she compared the scores of those who didn’t do their homework to those that did!

Learning Through An 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 gets 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. Before each session Patrick’s arms and back are covered in the muscle cream, while Sponge Bob’s arms and back are covered with the regular lotion.

What is the Control? 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.

Check for Understanding Mrs. Crespo 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 metal nails in. She then saw how many days it took each liquid to dissolve the nails. She also placed a metal 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.

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.