Lesson 6 Decontamination

Episode 1

Reasoning Resources: Worksheet 1, rulers, 1 cm squared gris on acetate
Whole class preparation: story to set up the Left-Right robot context
Programming a robot as a sequence of clear instructions for movement on a plane.

Recognising that left and right are relative, or dependent, on either the observing person or the moving object.

To programme a robot, you must place yourself in the position facing the way it is facing.
There is a desert island which developers want to turn into a holiday resort. But there is a problem: two sites of extremely dangerous toxic waste. The developers decide to use a robot to decontaminate the sites carefully. The robot will land on the island and will then need to be programmed to go to one of the toxic waste sites to spray the area. Next it will need to be directed back to the landing place to refill its spray before heading off to the other toxic waste site. Ask the class:If I were the robot, how could you give me directions to move from here to near John there? Ideas may include turning to the right direction, distance in steps or metres, forward/backwards, left/right, NESW. For example:‘take 4 steps’; ‘turn anti-clockwise’; ‘turn clockwise’; ‘go forwards, backwards, left or right’; ‘go 3 steps’; ‘East.’ Perform all pupils directions literally (including bumping into desks) showing where the instructions have to be precise.

After setting the scene, tell the class that the robot they will be using will only understand: Forwards, Backwards, Left (which means rotate 90° to the left), Right (rotate 90° to the right) and a distance (in this case, steps).

Now the pupils guide the teacher around the room, perhaps from the farthest corner to the door. It is helpful to include a situation where the teacher is amongst the pupils, and being asked to turn by someone facing them who gets the directions muddled up, since their ‘right’ is the teacher's ‘left. Discuss how to get the robot to turn 180° (L, L or R, R).
Pair/small group work

Deciding what information is needed to be able to solve a problem.

Recording moves involves both directions and distance.

Directions may be abbreviated, e.g. L/R or in full ‘Left and ‘Right'
Give out a copy of Worksheet 1 (the map of the island) to each pair. Explain that there are three possible landing sites available (shown on the map as A,B and C), that the toxic waste sites are marked (as 1 and 2) and that on the island there is a big lake that the robot can't cross.

You could suggest that the robot lands at A, or the class could agree a landing point, or each group could choose their own landing point. Tell the class that you are not expecting them to be able to solve the problem yet. Give them two minutes to discuss in groups what problems there are and what information you need from me to overcome them.

Pupils may raise, in their own words, issues on the scale of the drawing, how to orientate the map and which way the robot is facing when it starts. Typical ideas are:‘We don’t know about distance’; ‘We need lines like on a map’; ‘There are no gridlines’; ‘There are no points of reference’; ‘There isn't a key’; ‘We don’t know which way is north’

Now explain that the robot starts in the middle of the landing place, at an angle of 90°. Make available some rulers and some acetate grids. 1 square on the grid {or a 1cm ruler) is 100 m on the ground, Demonstrate writing a move with a turn, e.g. Forward 3, Right 2 (no need for writing ‘forward’ after a turn) with the return journey as Back 2, Right 3. (The robot returns to its original landing place before heading off to the next toxic site, to enable pupils to discuss ‘undoing’a set of actions.)

Pupils continue to work on guiding their robot in pairs. They can record their instructions on Worksheet 1, next to the map. Some pupils may orientate themselves so that they are facing the same way as the robot. Others may turn the paper after each move; this could form part of the whole class discussion. It is important that the return journey is worked out so that comparisons between the outward and return journeys can be made.
Whole class sharing/discussion
‘Undoing’ of two moves is logically similar to undoing

| think of a number’ type problems. In these, to work out the original number the inverse of each operation must be used and they must be employed in the reverse order. Here, the inverse of a forward move could be a back move or two turns.
Quickly notate the directions for the journey from A to 1 and back again. Ask for comments. Pupils may have spotted that the return journey has some similarities to the outward journey. The instructions are in reverse order and the turns have been changed. So the movement can be reversed from code alone: to reverse F15, R6 you could write B6, R15 or RR6, L15, or LL6 ,L15.

Give directions for a possible outward journey from A to 2 and discuss how to work out the return journey.


Thinking Mathematics Lessons Copyright © by Michael Shayer and Mundher Adhami. All Rights Reserved.

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