Variables in Your Science Fair Project
[Pages:7]Variables in Your Science Fair Project
Variables
Scientists use an experim ent to search for cause and effect relationships in nature. I n other words, they design an experim ent so that changes to one item cause som ething else to vary in a predictable way.
These changing quant it ies are called va r ia ble s. A variable is any fact or, t rait , or condit ion t hat can exist in differing am ounts or types. An experim ent usually has three kinds of variables: independent, dependent, and controlled.
The inde pe nde nt va r ia ble is t he one t hat is changed by t he scient ist . To insure a fair t est , a good experim ent has only one independent variable. As the scient ist changes t he independent variable, he or she obse r ve s what happens. To read m ore about perform ing a fair t est , visit and you will find t he " Variables for Beginners" link on t he Proj ect Guide page.
The scient ist focuses his or her observat ions on t he de pe nde nt va r ia ble t o see how it responds t o t he change m ade t o t he independent variable. The new value of t he dependent variable is caused by and depends on the value of the independent variable.
For exam ple, if you open a faucet ( t he independent variable) , t he quant it y of wat er flowing ( dependent variable) changes in response- - you observe t hat t he wat er flow increases. The num ber of dependent variables in an experim ent varies, but there is often m ore than one.
Experim ent s also have con t r olle d va r ia ble s. Cont rolled variables are quant it ies t hat a scient ist want s t o rem ain const ant , and he m ust observe t hem as carefully as t he dependent v ariables. For exam ple, if we want to m easure how m uch water flow increases when we open a faucet, it is im portant to m ake sure that t he wat er pressure ( t he cont rolled variable) is held const ant . That 's because bot h t he wat er pressure and t he opening of a faucet have an im pact on how m uch wat er flows. I f we change bot h of t hem at t he sam e tim e, we can't be sure how m uch of the change in water flow is because of the faucet opening and how m uch because of t he wat er pressure. I n ot her words, it would not be a fair t est . Most experim ent s have m ore than one controlled variable. Som e people refer to controlled variables as "constant variables."
I n a good experim ent, the scientist m ust be able to m easure the values for each variable. Weight or m ass is an exam ple of a variable t hat is very easy t o m easure. However, im agine t rying t o do an experim ent where one of t he variables is love. There is no such t hing as a " love- m et er." You m ight have a be lie f t hat som eone is in love, but you cannot really be sure, and you would probably have friends that don't agree with you. So, love is not m easurable in a scientific sense; therefore, it would be a poor variable to use in an experim ent.
Variables W orksheet
You can use t he Variables and Hypot hesis Worksheet t o help you develop your own plan. Your t eacher m ight have passed t his out t o you, or you can find it on t he Proj ect Guide's " Variables" page under " Relat ed Links" at .
Page 1 of 3
Exam ples of Variables
Qu e st ion
I ndependent Variable
Dependent Variables
Cont r olle d Va r ia ble s
( W hat I change)
How m uch water flows through a faucet at different openings?
Water faucet opening ( closed, half open, fully open)
( W hat I observe) Am ount of water flowing m easured in liters per m inute
( W hat I keep the sam e)
? The Faucet ? Water pressure, or how m uch the water is
" p u sh in g "
"Different water pressure m ight also cause different am ounts of water to flow and different faucets m ay behave differently, so to insure a fair test I want to keep the water pressure and t he faucet the sam e for each faucet opening that I test."
Does heating a cup of water allow it to dissolve m ore su g ar ?
Does fertilizer make a plant grow bigger?
Tem perat ure of t he water m easured in degrees Cent igrade
Am ount of sugar that dissolves com pletely m easured in gram s
Am ount of fertilizer m easured in gram s
? Growt h of t he plant
m easured by it s height
? Growt h of t he plant
m easured by t he num ber of leaves
? See Measuring Plant
Growt h for m ore ways to m easure plant growth
? Stirring ? Type of sugar
"More st irring m ight also increase t he am ount of sugar that dissolves and different sugars m ight dissolve in different am ounts, so to insure a fair test I want to keep t hese variables the sam e for each cup of water."
? Sam e size pot for each plant ? Sam e type of plant in each pot ? Sam e type and am ount of soil in each pot ? Sam e am ount of water and light ? Make m easurem ent s of growt h for each plant at t he
sam e t im e
" The m any variables above can each change how fast a plant grows, so to insure a fair test of the fertilizer, each of them m ust be kept the sam e for every pot."
Does an electric motor turn faster if you increase the v olt age?
Voltage of the elect r icit y m easured in volt s
Speed of rotation m easured in revolutions per minute ( RPMs)
? Sam e m otor for every test ? The m ot or should be doing t he sam e work for each
test ( turning the sam e wheel, propeller or w hat ev er )
"The work t hat a m ot or perform s has a big im pact on its speed, so to insure a fair test I m ust keep that variable the sam e."
Tim e as an Exam ple of an I ndependent Variable
I n som e experim ent s, t im e is what causes t he dependent variable t o change. The scient ist sim ply st art s the process, then observes and records data at regular intervals.
Qu e st ion
I ndependent Variable
Dependent Variables
Con t r olle d Va r ia ble s
How fast does a candle burn?
( W hat I change) Tim e m easured in m inutes
( W hat I observe) Height of candle m easured in centim eters at regular intervals of tim e (for exam ple, every 5 m inutes)
( W hat I keep the sam e)
? Use sam e t ype of candle for every t est ? Wind--m ake sure there is none
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The I ndependent Variable for Surveys and Tests of Different Groups
When a scientist perform s a test or survey on different groups of people or things, those groups define the independent variable. For exam ple:
Qu e st ion
Who list ens to m usic the m ost: teenagers or their parents?
I ndependent Variable
Dependent Variables
Con t r olle d Va r ia ble s
( W hat I change) The groups receiving the survey: t eenagers or parents
( W hat I observe) The am ount of t im e t hat each person list ens to m usic per day m easured in hours
( W hat I keep the sam e) Ask the quest ion in exact ly t he sam e way to each individual
Eit her/ Or ( Binary) Variables
Som et im es a variable sim ply represent s an eit her/ or ( binary) condit ion. For exam ple, som et hing m ight be either present or not present during an experim ent.
Qu e st ion
I s a classroom noisier when the teacher leaves the room ?
Do bicycle fenders keep the rider dry when riding through a puddle?
I ndependent Variable
Dependent Variables
Con t r olle d Va r ia ble s
( W hat I change) Teacher locat ion: The teacher is either in the room or not in the room .
"The t eacher's locat ion is an either/ or situation" Fenders: The bicycle either has fenders or it does not
"Many engineering proj ects have alternative designs with independent variables like this one (with and without fenders) ."
( W hat I observe) Loudness m easured in decibels
The rider eit her get s wet or does not "Dependent variables can represent either/ or situations, too."
( W hat I keep the sam e)
? Sam e classroom ? Sam e students ? Sam e tim e of day
? Sam e type of bike and tires ( except
for the fenders!)
? Riding at t he sam e speed ? Sam e size and depth of puddle
Sam ple
To see a sam ple cont aining t he variables and hypot hesis, visit and you will find t he " Sam ple Variables and Hypot hesis" link on t he Proj ect Guide's " Variables" page under " Relat ed Links."
Scie nce Fa ir Pr oj e ct Va r ia ble s Che ck list
W hat Makes for Good Variables?
I s the independent variable m easurable? Can you change t he independent var iable during t he experim ent ? Have you identified all relevant dependent variables, and are they all caused by and dependent on the independent variable? Are all dependent variable( s) m easurable? Have you identified all relevant controlled variables? Can all cont rolled variables be held at a st eady value during t he experim ent ?
For Good Variables, You Should Answ er "Yes" t o Every Quest ion
Yes / No Yes / No Yes / No
Yes / No Yes / No Yes / No
Page 3 of 3 Copyright ?2008 Kenneth Lafferty Hess Family Charitable Foundation. All rights reserved. . You may print and
distribute up to 200 copies of this document annually, at no charge, for personal and classroom educational use. When printing this document, you may NOT modify it in any way. For any other use, please contact Science Buddies. 2008/09/13
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