Let’s Think Secondary Maths, Lesson 6 - Decontamination
Overview
Thinking Strands: spatial representation (relative and absolute systems of orientation).
In Decontamination learners practice using two different forms of direction: left/right (relative)
and compass (absolute). By guiding two robots using these different methods learners consider
the pros and cons of each and are led to consider the continuous measurements of angles and
vectors.
Aims
 To understand the difference between relative and absolute systems of orientation.
 To apply the continuous nature of the compass system to describing movement in vectors.
Vocabulary
Relative, absolute, compass (N, S, E, W), angles, degrees + various other words to describe
giving directions, scale.
In-school resource preparation
Materials – Supplied
 Resource Sheet A: The desert island (Hook)
 Resource Sheet B: Desert island template – copied to A3.
 Resource Sheet C: Giving directions challenge (not yet written).
Materials – Not supplied
 Compasses, rulers, blindfolds.
Note – this lesson is easily adapted to a variety of contexts and could be carried out outside on
the yard or playing field. The task is quite one given the number of landing points and the two
sources of pollution. The aim is for the learners to realise, for many this will be the first time, the
difference between the relative and absolute systems.
Hook: The illustration sets the scene for the narrative; two people find a desert island and
wish to develop it. The problem is that there is some nuclear waste that needs decontaminating.
The friends wish to develop the island as a resort and decide to use robots to carry out the work
and they have two to choose from: a left/right and a compass robot. Spend a few moments
discussing how instructions might be given to each robot (explain that the compass robot always
starts pointing north and then turns the required distance clockwise).
Activity 1: Show learners the island template, quickly explaining the three possible landing
points and the two areas of pollution. Ask the class to direct the left/right robot without letting
them know that the map has no scale and so it is impossible to provide adequate directions. How
long you let this activity develop is dependent upon the class and it may be that you wait until the
learners themselves raise the issue. If not simply draw the class together asking them to share
what they have done – it will quickly become apparent that they need to know how big the island
is if they are to complete the task. Upon conclusion tell the class that each cm = 1km and direct
them to draw their own grids on the island to help the left/right robot.
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Activity 2: Learners can now direct both robots around the island starting with the left/right
robot. If done fully this activity could take more than 2 hours – simply ensure they have had a
chance to direct both robots and have discussed the difference between them. To focus the
discussion ask the following question; ‘Which robot do you think is best for the developers?’
Time is needed here to allow the range of ways the learners will describe the two different forms
of giving direction – begin with a vote and then allow the groups to share the reasons for their
choices (see video tutorial for details of how to develop this discussion).
The compass robot can then be used to move the pupils towards vectors via the question(s); ‘How
could we make the compass robot even easier to use? If we had no grid lines how else could we
move the compass robot?’ This activity could form the basis of a homework or follow up lesson
if used to start a topic on bearings.
End of activity reflection: Encourage the learners to consider the new ideas they will have
come across. For many they will not have considered the difference between relative (left/right)
and absolute (compass) before and so they will need time to reflect upon this and to put their
understanding of this into words. The giving directions challenge question sheet can be used as a
homework activity or to further encourage the learners to reflect upon the learning within
Decontamination.
Notes
During joint planning ensure you:
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