Revise the properties of a square. Recap how turtle draws a square and equilateral triangle. Remind pupils of the REPEAT command.
Is a square a rectangle? Why?
What is the sum of the internal angles? What do two / three angles add up to?
Are these shapes squares? Why / why not?
Key vocabulary
Regular polygon, pentagon, hexagon, heptagon, octagon, nonagon, decagon, dodecagon
Main activity
How are we going to tell the turtle draw a hexagon? Start with the turtle facing up the screen. Draw the first side. The turtle now has to face which direction? What angle does it turn through?
When the hexagon is complete, check that the turtle is facing its original heading. What is the total of the turns it has made?
Groups work on available computers. Individuals work on paper grids, with a table to record their findings. First, they investigate a regular octagon. Can they see the connection between number of sides and the turtle turn?
If the turtle repeatedly moves forward the same distance then RT 30, what polygon will it draw? (dodecagon, 12 sides)
Support
Ask children to mark on the sheet, then measure, the angle which the turtle turns when it draws the square, triangle and hexagon. Plastic or card shapes will help children to touch and hold, as well as see the corners.
Challenge
Work out the instructions for a pentagon, nonagon, decagon.
Plenary
Look at the completed table:
|
Name
|
Number of sides
|
Turn (degrees)
|
Total turn
|
|
equilateral triangle
|
3
|
120
|
360
|
|
square
|
4
|
90
|
360
|
|
hexagon
|
6
|
60
|
360
|
|
octagon
|
8
|
45
|
360
|
What is the rule for telling the turtle to draw a regular polygon? How do we draw a pentagon? Test some of the children's suggestions.
Computer groups: how could we draw a circle (or a shape with so many sides it looks like a circle)?
Arrange times before the next lesson where all children can try their instructions on the computer.
