The Key to a Good Experiment

Controlling the Variables

Every Experiment has Two Key Parts

Constants• Constants are the things you control so that they don’t change during

your experiment. • Usually, you want everything in your experiment to remain constant

except one variable. • This is the one thing you want to change so you can see what effect that

change has on your result.

Variables• Are the things that change

during an experiment.

• If you plan your experiment correctly, the one variable is the thing you are testing. It changes because you want it to.

• If you don’t, it is something that you did not want to have change. When this happens your experiment is messed up.

For ExampleSuppose you want to test if Wiley Coyote’s

favorite “El Cheapo” batteries made by ACME will last as long as the “Energizer

Bunny” brand.

You figure you will buy batteries of both types and put them in flash lights and see

how long the lights stay on.

against

Sounds like a good plan. But what is the variable you

want to test?

The BRAND, right?

This variable the one you change

is called theINDEPENDENT

variable

BUTand this is a big but

What other variable might affect the results of your experiment?

How about

• The AGE of the batteries. If you buy brand new El Cheapos and compare it against 50 year old Energizers, would that be a good test? Why not?

I am way too tired for this!

He thinks he’s tired?

What if you used a GIANT size El Cheapos and AAA size mini

Energizers?

El GrandoCheapo

Way too small

What if the flashlights were different types and one had a big

bulb that needed more energy and the other a little bulb that

needed very little?

The Problem With All These Experiments Is That You Have

More Than One

Variable

• In your first experiment you have added the age of the battery as a variable. So now you can’t tell if it was the age or the brand that made the difference.

• In your second experiment you added the size of the battery as a variable.

• In the third, you added bulb size.

Remember That You Want to Find Out How BRAND Affects Battery Life.

This Should Be Your ONLY Variable.

As a Result of Not Controlling Every Variable Except Brand

Your Experiment is Worth Exactly

Diddly Squat!

Goose Egg!

Nothing!

Nada!

0

So in this example how do you

control the variables ?

By making them constants!

So, once you finish your controlled experiment you will get results in the form of data.

The results are called the

DEPENDENT VARIABLEDependent because they depend on what you do to your independent variable and variable

because they change.