Control Variable

Variables, Constants, Control Groups, Experimental Groups

What are they?

Multiple Choice

Quick Review: An independent variable in an experiment is the thing we...

• Measure

• Change

• Keep the Same

• Build

I.V. = The temperature outside

This is the ONLY thing I can change in my experiment!!!

Multiple Choice

A dependent variable is the thing we...

• Measure

• Change

• Keep the Same

• Observe

Let’s Start with Constants

• Controlled S.M. experiments = cause & effect

• How does [independent variable] affect [dependent variable]?

• In a controlled experiment, we can only ever change one thing at a time. This is our independent or manipulated variable

• Ex: How does sunlight affect plant growth?

• I can ONLY change the amount of sun each plant gets and NOTHING else, or my experiment isn’t valid!

Constants

• Because we can only change one thing, every other part of our experiment must be kept the same.

• Constants = the things we keep the same in an experiment so that we only change ONE thing [I.V.]

Multiple Choice

How many things can we change in an experiment?

• None

• Two

• One

• Three

• As many as we want

Without constants, we get error!

• Was it the independent variable or something else that caused the outcome of our experiment? 

• If we allow more than one thing to be changed, we’ll never know!

• Error = something besides our I.V. affecting our experiment results

Example of Constants

• My testable science question:

• Does the temperature outside affect how high my kite will fly?

Multiple Choice

What's the independent variable: Does the temperature outside affect how high my kite will fly?

• The kite

• How high the kite will fly

• The temperature outside

• The wind speed

Multiple Choice

What's the dependent variable: Does the temperature outside affect how high my kite will fly?

• The kite

• How high the kite will fly

• The temperature outside

• The wind speed

As a control-freak scientist, I have to ask myself: what else besides the independent variable could affect my dependent variable, even accidentally?

These are constants, or things we need to keep the same during our experiment.

We can ONLY change the temperature outside, so wind speeds, geographic location (where I’m standing), which kite I use, what time of day it is, the humidity/ moisture in the air, birds running into my kite, whether other people are also flying kites, etc. all need to STAY THE SAME!!!

Multiple Select

If we don't pay attention to constants in our experiment, what could happen? Check all that apply.

• We could have error

• More than one thing could affect the dependent variable

• We won't know if our results are truly based on the independent variable or something else

• Our results will be inaccurate

• Nothing will happen

Multiple Choice

Which brand of gum, Hubba Bubba or Double Bubble, results in bigger bubbles blown? What's our dependent variable?

• Brand of gum

• Color of gum

• Size of bubble blown

• Time we chew the gum for

Control & Experimental Groups

Control & Experimental Groups

• When we design a controlled experiment, we want to see how one independent variable affects a dependent variable.

• (How does the air temperature affect how fast ice melts?)

We only want to measure one IV, so we brainstorm all the constants that could affect our experiment (even accidentally).

• Location of ice, surface the ice is sitting on/ in, size of the ice, airflow in the room, temperature of the container when we put the ice in, the timer we use, the person doing the timing, the thermometer we use, the person holding/ reading the thermometer, etc.

To make sure we didn’t miss anything, though, we will use a control group.

Experimental Group

• An experimental group is whatever you’re experimenting on; gets the I.V. 

• In our ice example, the ice that we’re exposing to different air temperatures

Control Group

• A control group is another group of whatever you’re experimenting on, and is identical to the experimental group EXCEPT: you do NOT change the independent variable!

• The control group gets all the same constants as the experimental group

• Constants in our ice example, same container, same airflow, same room, timer, thermometer, etc.

Multiple Select

What are the two groups in a controlled experiment called?

• Control Group

• Change Group

• Experimental Group

• Observe Group

Multiple Choice

The group that does receive the independent variable change is the

• Control Group

• Experimental Group

Multiple Choice

What do the experimental and control groups in an experiment NOT have in common?

• They use the same materials

• The dependent variable (what we're measuring) is the same for both groups

• The independent variable (what we're changing) is the same for both groups

• The constants (except the I.V.) are the same for both groups

• We collect the same data for both groups

Experimental Group

• Gets the independent variable (I change the amount of water) and all the constants

Control Group

• Gets all the constants PLUS the I.V. becomes a constant (each plant gets the same amount of water) 

My Experimental Design

My CG should have the same results as WHICH plant in my EG?

Multiple Choice

My control group plants should show the same results as which plant in my experimental group?

• Plant 1

• Plant 2

• Plant 3

My Experiment Results

CG as expected; data looks accurate!

Something is wrong... CG inconsistent!

Constants

• Controlled Experiments = How does [independent variable] affect [dependent variable]?

• We only change ONE thing in a controlled experiment - only ONE independent variable

• Constants are all the things/ conditions we keep the same in an experiment so the ONE I.V. is the only thing that’s changed

Control Groups

• 2 groups in an experiment: experimental group & control group

• The experimental group IS manipulated/ gets the independent variable

• Control groups get all the same constants as the experimental group, PLUS they DON’T get the I.V. or the I.V. becomes a constant.

Multiple Choice

A plant receives the same amount of sunlight and water at the same time each day. What is the constant?

• different amount of sunlight

• different plant

• same amount of sunlight, water and same time

Multiple Choice

Jerry believed that fertilizer will make the plant grow faster, so he treated one plant with fertilizer and the other plant did not receive fertilizer. What is the experimental group?

• plant receiving fertilizer

• plant not receiving fertilizer

• plant receiving water because it needs water to grow

Control Group

• Does not receive the treatment or test material

• For example: One plant does not receive fertilizer

• Not receiving the fertilizer makes this plant the control group

Multiple Choice

Michael believed that fertilizer will make the plant grow faster, so he treated one plant with fertilizer and the other plant did not receive fertilizer. What is the control group?

• plant receiving fertilizer

• plant not receiving fertilizer

• Michael believing the plant will grow faster

Multiple Choice

A test is set up to test which brand of soda creates the biggest foam explosion when adding a Mentos candy.  Three different sodas were tested. They measured the height of the foam eruption.   What is a controlled variable (constant) for this experiment?

• Brand of soda
• Number of mentos candies used
• Height of foam eruption
• All are controlled variables (constants)

In an experiment, the group that is being treated by the independent variable is the experimental group.

The control ​group is the one allows for comparisons.

​Experimental vs. Control Groups

Multiple Choice

If I study for my scientific method test, then I will have a better test score. Who would be in the control group?

• Scientific Method
• Everyone that studies and doesn't study

• The students that study.

• The students that don't study.

Multiple Choice

Research Question: Does using a higher quality of gasoline in a car effect how fast the car can drive. What is the experimental group in this experiment?

• cars with regular unleaded gasoline

• cars with higher quality gasoline

• electric cars

• gasoline-powered cars

Multiple Choice

The part of the experiment that remains the same for the control and experimental group.

• constants
• control
• independent
• dependent

Multiple Choice

Suppose you are looking at how daisies grow in different light sources. What would your control group be?

• Blue filtered light
• Red filtered light
• Green filtered light
• Sunglight

Multiple Choice

The control group is the...

• group you are testing
• "normal" group

Most people mix these up because...

• They sound the same

• They both have to do with experiments

• They are closely related, but not identical

• Scientists insist on calling constants “controlled variables” sometimes, which makes it even more confusing