Introduction to variables

A variable is anything that can change. However, in mathematics this term is often used for any letter which is used in place of a number. Many mathematics teachers prefer to call such letters 'placeholders' because they aren't really able to change in the way that scientific variables can. In science there are three main types of variables, namely:

Independent variable: The thing you change

Dependent variable: The thing you measure

Control variables: The things that stay the same.

This video (3:41) is a good introduction to variables in science.

Fair tests

A fair test is a scientific experiment where you change only one thing (i.e., the independent variable) and measure the result (i.e., the dependent variable), while keeping all other conditions exactly the same. This ensures that any changes you see are caused only by the single factor you altered. Cows Moo Softly is a saying which is sometimes used to help young learners remember the steps in a fair test. The C in cows is for 'change', the M in moo is for 'measure', and the S in softly is for 'same'. The following diagram illustrates this.

(Image source http://downunderteacher.blogspot.com/2012/01/freebie-science-variables-and-job-roles.html)

Independent variables 

In science experiments, the independent variable is the thing that you change.

Dependent variables

In science experiments, the dependent variable is the thing that you measure.

Control variables

In science experiments, the control variables are the things that remain the same.

More on fair tests

This video (3:45) has a good example of a fair test using some common kitchen ingredients such as baking soda and three different types of vinegar.

Projectile investigation

The following investigation involves air rockets but it would be more precise to call these 'rockets' projectiles. This is because there is no fuel to keep the rocket moving after the initial launch force provided by your foot pushing down on the air as shown in the short video (0:08) below.

The image below shows that 45 degrees should give you the longest distance.

The projectile below is set to launch at 40 degrees.

Note: Although 45 degrees should give you the greatest distance, in sports such as golf you would also need to consider that rolling is part of your objective as it is about where the ball lands, but also, where the ball comes to rest. Due to the design of various gold clubs (such as drivers) the angle is often much smaller than 45 degrees.

Investigation steps

• This investigation is about verification to test the following hypothesis; "If the projectile is launched at an angle of 45 degrees, then it should go further than all other angles".
• Each student gets to launch three projectiles.
• A student, helper or teacher can help set the angle depending on the angles specified by the student.
• The first angle should less than 45 degrees, the second angle should be equal to 45 degrees, and the third angle should be greater than 45 degrees.
• A long tape measure is left on the ground to show the distances of each projectile. The readings are best taken by a student, helper or teacher who can read the distances quickly and accurately.
• The data for each launch is called out by the reader and then entered by a different student so the launching student can focus on placing each projectile on the tube and launching it.
• Other students can be responsible for fetching the projectiles.
• Everyone takes turns with the tasks listed above.
• As this is an outdoor activity, it is recommended that the following table be mounted on a clipboard for the data collection.
• An A4 PDF of this table is available here.

Was this a fair test? Why/why not? Which elements of the air rocket activity fit the criteria for fair tests? Which elements cannot be easily controlled?

Reflex activity

This activity can be done in pairs using a ruler, paper and a pencil.

• One student holds a ruler upright with zero at the bottom.
• The other student places their thumb and index finger apart on either side of the zero.
• The student holding the ruler releases the ruler without warning.
• The other student catches the ruler by bringing their thumb and index finger together.
• This activity could be conducted as a standalone experiment or repeated at different times of the day to compare reflexes at different times such as morning and afternoon.
• A table would be a logical way to record the data.
• A bar graph would be a logical way to compare the data if contrasting morning and afternoon.
• The data would be more accurate by averaging multiple measurements.

Correlation across data sets

Sometimes there might seem to be correlations across data sets which are best described as coincidences such as in the following example:

Articulating a continuum of learning for fair tests

A continuum of learning for fair tests on a scale of 1 to 10 could be benchmarked as follows:

A student: (1) defines a variable; (2) outlines the requirements of a fair test; (3) can discuss the requirements of a fair test from memory in any order; (4) can explain why the independent variable is the focus of an experiment; (5) can measure the dependent variable and relate this measurement to the independent variable; (6) can explain why an experiment is only a fair test if the control variable(s) can be kept constant; (7) designs their own fair test; (8) writes instructions for their fair test with clearly defined variables; (9) formulates a hypothesis for their fair test; (10) can explain the relationship between fair tests and hypotheses.

We welcome your feedback and suggestions

The chief investigator for The SILO Project is Associate Professor Brendan Jacobs, Head of Department STEM Education, University of New England. The SILO Project thrives on incremental improvement so constructive feedback is greatly appreciated. Please contact Brendan via email at bjacobs7@une.edu.au to share your thoughts and recommendations.

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