Lesson Notes By Weeks and Term v5 - Grade 4
Geometry: 2D shapes and symmetry – Week 7 focus
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Geometry: 2D shapes and symmetry – Week 7 focus
Download the Lessonotes Mobile South Africa app for faster lesson access on Android and iPhone.
Subject: Mathematics
Class: Grade 4
Term: 2nd Term
Week: 7
Theme: General lesson support
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This week, we're diving into the exciting world of geometry! We'll be exploring 2D shapes and discovering what makes them special. 2D shapes are everywhere around us, from the tiles on your bathroom floor to the shapes on a Stop sign. Understanding 2D shapes helps us describe and understand the world around us. We'll also learn about symmetry, which is all about balance and beautiful patterns. Knowing about symmetry helps us understand design and appreciate the beauty of things like butterflies and traditional Zulu beadwork.
2D Shapes 2D shapes are flat shapes that only have two dimensions: length and width. They don't have any thickness.
Let's look at some common 2D shapes: Square: A square has four sides, and all four sides are equal in length. It also has four corners, which are all right angles (like the corner of a book).
Rectangle: A rectangle also has four sides and four corners that are right angles.
However, unlike a square, a rectangle only has two pairs of equal sides. The opposite sides are equal in length.
Triangle: A triangle has three sides and three corners.
There are different types of triangles: Equilateral triangle:* All three sides are equal.
Isosceles triangle:* Two sides are equal.
Scalene triangle:* No sides are equal.
Right-angled triangle:* One angle is a right angle (90 degrees).
Circle: A circle is a round shape with no sides or corners. All points on a circle are the same distance from the centre.
Pentagon: A pentagon has five sides and five corners. Think of the building "The Pentagon" in America – it has five sides!
Example 1: Imagine a tile on your kitchen floor. If all the sides are the same length, and the corners are perfectly square, it's likely a square. If two opposite sides are longer than the other two, it's probably a rectangle.
Example 2: A street sign shaped like a triangle is warning you about something. Pay attention to the shape and the picture inside it! Symmetry Symmetry means that a shape can be folded in half so that both halves match perfectly. The line where you fold the shape is called the line of symmetry or the axis of symmetry.
Line of Symmetry: An imaginary line that divides a shape into two identical halves.
Example 1: Imagine a butterfly. If you draw a line down the middle of its body, the left wing looks exactly like the right wing. This means the butterfly is symmetrical, and the line down its body is the line of symmetry.
Example 2: A square has four lines of symmetry. You can fold it in half vertically, horizontally, or diagonally, and the two halves will match perfectly.
Example 3: A rectangle has two lines of symmetry: one vertical and one horizontal. You can't fold it diagonally and have the sides match.
Example 4: A circle has an infinite number of lines of symmetry! You can draw a line through the centre of the circle in any direction, and the two halves will be the same.
Example 5: Not all shapes are symmetrical. Think of the shape of the province of KwaZulu-Natal. You cannot draw a line down the middle so both sides match – it is NOT symmetrical. Drawing 2D Shapes To draw accurate 2D shapes, you will need a ruler and a pencil.
For squares and rectangles: Use the ruler to measure the length of each side and draw straight lines connecting the corners. Make sure the corners are right angles.
For triangles: Use the ruler to measure the length of each side. If you are drawing a right-angled triangle, use the corner of a book or a set square to make sure the right angle is accurate.
For circles: You can use a compass to draw a perfect circle. Place the point of the compass where you want the centre of the circle to be, and then rotate the pencil around the point. You can also trace around a circular object.
For Pentagons: This can be tricky to draw perfectly freehand. Use a protractor to help you ensure the angles are equal, or look up a template online to use as a guide. Guided Practice (With Solutions)
Question 1: Identify the following shape and describe its properties: [Image of a square] Solution: Shape: Square Properties: It has four sides, all of which are equal in length. It also has four corners, which are all right angles.
Question 2: Draw a rectangle with a length of 6cm and a width of 3cm.
Solution: Use your ruler to draw a line that is 6cm long. This is the length of the rectangle. At each end of the line, use your ruler to draw a line that is 3cm long, making sure the lines are at right angles to the first line. This is the width of the rectangle. You can use the corner of a book to ensure the angles are right angles. Connect the ends of the 3cm lines to complete the rectangle. The opposite side should measure 6cm.
Question 3: Does the following shape have a line of symmetry? If so, draw the line of symmetry. [Image of an isosceles triangle] Solution: Yes, it has one line of symmetry. Draw a line from the top point (vertex) of the isosceles triangle down to the middle of the opposite side (base). This line divides the triangle into two identical halves.
Question 4: Thando drew a shape. It has 5 sides and 5 corners. What shape did Thando draw?
Solution: Thando drew a pentagon. A pentagon is a shape with 5 sides and 5 corners.
Question 5: Draw a square and then draw all of its lines of symmetry. How many lines of symmetry does it have?
Solution: Draw a square. Draw a line vertically down the middle. Draw a line horizontally across the middle. Draw a line diagonally from one corner to the opposite corner.