Lesson Notes By Weeks and Term v5 - Grade 4

Lesson Video

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Performance objectives

• Identify and name common 2D shapes and their properties.
• Draw 2D shapes accurately.
• Define symmetry and find lines of symmetry.
• Tell the difference between symmetrical and non-symmetrical shapes.
• Create your own symmetrical patterns.

Lesson summary

This week, we dive into the exciting world of 2D shapes and symmetry! Geometry helps us understand the world around us. From the rectangular shape of our classroom door to the triangular shape of the roof of a shack, understanding shapes is crucial. Symmetry is also everywhere! Think about how the left and right sides of your face are almost mirror images, or the beautiful patterns on a butterfly's wings. Learning about shapes and symmetry helps us develop spatial reasoning skills, which are important for everything from packing a school bag efficiently to understanding maps and building structures.

Lesson notes

2.1 2D Shapes: Flat Figures with Length and Width 2D shapes are flat shapes that only have two dimensions: length and width. They lie on a flat surface, like a piece of paper or the chalkboard.

Circle: A round shape with no corners or sides. All points on the circle are the same distance from the center. Imagine a plate of pap or a 5 Rand coin.

Square: A shape with four equal sides and four right angles (90 degrees). Think about a chess board square.

Rectangle: A shape with four sides and four right angles. Opposite sides are equal in length. A door or a classroom window often forms a rectangle.

Triangle: A shape with three sides and three angles. There are different types of triangles (e.g., equilateral – all sides equal, isosceles – two sides equal, scalene – no sides equal). Consider the shape of a slice of watermelon.

Properties of 2D Shapes: Sides: The straight lines that form the shape.

Vertices (Corners): The points where the sides meet. (Singular: vertex)

Example 1: Analyzing a Rectangle A rectangle has four sides. Let's say the length of the rectangle is 10cm and the width is 5cm. It has four vertices.

Opposite sides are equal: two sides are 10cm each, and the other two sides are 5cm each. All four angles are right angles (90 degrees).

Example 2: Analyzing a Triangle A triangle has three sides and three vertices. If it's an equilateral triangle, all three sides are the same length, and all three angles are the same size (60 degrees). If it's a scalene triangle, all the sides and angles are different. 2.2 Symmetry: Mirror Images Symmetry means that a shape looks exactly the same on both sides of a dividing line. This dividing line is called the line of symmetry or mirror line. If you were to fold a symmetrical shape along its line of symmetry, the two halves would match perfectly.

Line of Symmetry: An imaginary line that divides a shape into two identical halves.

How to Identify Symmetry: Visualize: Imagine folding the shape along a line.

Check: Do the two halves match exactly? If they do, the line is a line of symmetry.

Example 1: Symmetry in a Square A square has four lines of symmetry: One vertical line down the middle. One horizontal line across the middle. Two diagonal lines from corner to corner.

Example 2: Symmetry in a Rectangle A rectangle has two lines of symmetry: One vertical line down the middle. One horizontal line across the middle. (It does not have diagonal lines of symmetry unless it is a square).

Example 3: Symmetry in a Circle A circle has an infinite number of lines of symmetry, as you can draw a line through the center from any direction and the two halves will match.

Example 4: Non-Symmetrical Shapes Some shapes have no lines of symmetry. An irregular shape (a shape with sides and angles that are not equal) is often non-symmetrical.

Practical Activity: Finding Lines of Symmetry Give learners various cut-out shapes (square, rectangle, circle, triangle, heart shape) and ask them to fold each shape to find all the lines of symmetry. They can draw the lines of symmetry using a ruler. Guided Practice (With Solutions)

Question 1: Identify the shape and state how many sides and vertices it has: [Image of a Square] Solution: The shape is a square. It has 4 sides and 4 vertices (corners). All sides are equal in length, and all angles are right angles.

Question 2: Draw a rectangle with a length of 8cm and a width of 4cm using a ruler.

Solution: Draw a straight line 8cm long using a ruler. At each end of the line, draw a line perpendicular (at a right angle) to the first line. These lines should be 4cm long. Connect the top ends of the two 4cm lines to complete the rectangle. This line should also be 8cm long.

Commentary: Emphasize the use of the ruler for accurate measurement and ensuring right angles.

Question 3: Does this shape have a line of symmetry? If so, draw the line of symmetry. [Image of an isosceles triangle with the apex pointing upwards] Solution: Yes, the shape has one line of symmetry. Draw a vertical line from the top vertex (corner) down to the midpoint of the base. This line divides the triangle into two identical halves.

Question 4: Which of these shapes is NOT symmetrical? a) Circle b) Square c)

Scalene Triangle d)

Rectangle Solution: The answer is (c) Scalene Triangle. A scalene triangle has no lines of symmetry because all of its sides and angles are different. Circles, squares and rectangles (generally) are symmetrical. Independent Practice (Questions Only) Name three objects in the classroom that are shaped like rectangles. Draw a circle and show as many lines of symmetry as you can. Draw a square and a rectangle. Compare and contrast their properties (sides, vertices, angles, lines of symmetry). Draw a picture of a house using only squares, rectangles, and triangles. Which of the following shapes are symmetrical? (Provide images of a star, a heart, the letter 'A', and the number '3').