Lesson 2 Two variables
1 Remind pupils of the last lesson on variables, and relationships between variables. Two new examples are given on an OHP Master. Choose some examples from their regular science lessons to illustrate the use of these terms.
In this lesson, they are going to investigate variables further and do some investigations in which one variable is changed and they see what happens to another. The variable that the investigator (pupil or teacher) changes is called the input variable. The input variable is the one we have some control over. For instance, if we add more weights, weight is an input variable because we can decide whether or not to make it heavier.
The other variable, the one that changes as a result of what we do, is the outcome variable. If you add weights to a spring, then the extension of the spring would be the outcome variable. (10 minutes)
2 Divide the class into groups, point out the four investigations and explain how they are to do each in turn, as a ‘circus’. It does not matter which order they do them in. They will only have 5 minutes to look at each. The copies of Workcard 2D can be used as groups finish and are waiting to move to a new investigation. The emphasis is on the variables and the relationship between the variables in each activity, although some useful content may be learned as a byproduct. (30 minutes)
1 The pulley is straightforward: increasing the value of the input variable increases the value of the outcome variable.
2 For liquid heights, you may have to suggest that they write their results in order of increasing diameter, to see the pattern that as diameter goes up, height goes down.
3 ‘Leaves’ is the most difficult activity. The input variable is ‘side with Vaseline’, and the outcome is ‘dryness’ or any other words the pupils use to describe appearance. Pupils must use the idea that water cannot be lost through Vaseline and deduce from which side a leaf normally loses most water.
4 The height and weight of children in this example illustrates no relationship.
Furthermore, either could be the input or outcome variable. It depends on an initial ‘cause–effect’ hypothesis.
3 When at least two-thirds of the groups have done all activities, discuss the investigations, involving as many individuals as possible in telling the class about their answers and about their thinking. Do not go through each activity one by one but instead pick out some general questions to provoke metacognition such as:
Could you easily identify the inputs and outcome variables in each activity? Which ones were difficult? Why?
Did all the activities show relationships between variables? Which variables were related or linked together in activities 1, 2, 3 and 4?
Which did you find the hardest activity to think about? Why?
For pupils who feel anxious if they do not have the right answers for their Notesheets we suggest putting up a completed Notesheet on the overhead projector and letting the groups correct their own Notesheets. (10 minutes)
4 Recall other science activities they have done and question the input and outcome variables involved. This is bridging. (5 minutes)