Resources
Large display (see weekly plan) with marker pens.
The class will record work on plain paper.
Revision / oral
Look at the table from the last lesson. Recap the polygon rule: divide 360 by the number of sides to calculate the turtle turn. Review computer work. What is the angle to draw a 20-sided shape? A 15-sided shape? Why did we avoid a heptagon? (Logo will accept non-integral values, so this could be drawn!)
Key vocabulary
Factor, multiple, program
Main activity
Ask how we might draw a zig-zag. Model with a pen on the board first.
One possibility is REPEAT 4 [FD 50 RT 90 FD 50 LT 90].
What will happen if we make the left turn smaller?
Try these:
REPEAT 4 [FD 50 RT 90 FD 50 LT 45]
REPEAT 4 [FD 50 RT 150 FD 50 LT 105]
How many repeats will complete the star? How many points will it have? Draw attention to the difference between the right and left turn: what do children notice? (It is 45 in each case.) Can they suggest other 8-pointed stars?
NB Show how to review and repeat previous commands. 'How to...' sheet is attached.
Groups work on available computers. Individuals work on paper: write programs for different eight-pointed stars.
Support
Give children a printed copy of the 'bent zig-zags' above. 'Walk' them with a pencil. Write each move the turtle makes, without using REPEAT. Discuss what is being repeated each time. Ask children to draw what will happen if the turtle carries on repeating.
Challenge
Write programs for stars with six points, nine points.
Plenary
What is the rule for telling the turtle to draw an eight-pointed star? Six-pointed star? Nine-pointed star? Can we suggest angles for other types of star? Test some of the children's suggestions.
Quick-fire questions: 'Eight-pointed star, right turn 130 degrees, left turn - what?'
Arrange times before the next lesson where all children can try their programs on the computer.
