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 using a ruler.
• Identify and draw lines of symmetry in 2D shapes.
• Distinguish between symmetrical and asymmetrical shapes.
• Create symmetrical patterns using 2D shapes.

Lesson summary

Geometry helps us understand the world around us. From the shape of our classrooms and houses to the patterns in traditional African crafts, shapes and symmetry are everywhere! In this week's lesson, we will be exploring 2D shapes like squares, rectangles, triangles, and circles, and we'll learn about what makes them special. We will also learn about symmetry - that is, shapes that look the same on both sides if you cut them in half. Understanding these concepts helps us describe and appreciate the beauty and order in our world. Think of the intricate beadwork of Zulu culture, the geometric patterns in Ndebele art, or the way bees build hexagonal honeycombs - geometry is all around us!

Lesson notes

2D Shapes (Two-Dimensional Shapes): 2D shapes are flat shapes that have length and width but no thickness. They exist on a flat surface, like a piece of paper or a whiteboard. We are going to focus on four common 2D shapes: Square: A square has four straight sides that are all equal in length. It also has four corners, which we call vertices (singular: vertex). Each corner is a right angle (like the corner of a book).

Example:* The face of a dice is a square. A tiled floor often has square tiles.

Rectangle: A rectangle also has four straight sides and four vertices.

However, unlike a square, the opposite sides of a rectangle are equal in length, but not all four sides are equal. It also has four right angles.

Example:* A door, a window, and a chalkboard are often rectangles.

Triangle: A triangle has three straight sides and three vertices. There are different types of triangles (we will learn more about these in later grades). For now, let's focus on any shape with three sides.

Example:* The yield sign on the road is a triangle. Samosas (a popular snack) are often triangular.

Circle: A circle is a round shape with no straight sides and no vertices. It's defined by a single curved line that is always the same distance from the center.

Example:* A wheel, a coin, and the sun are all circles.

Properties of 2D Shapes: Properties are the things that make a shape what it is.

For example: Number of Sides:* How many straight edges does the shape have?

Number of Vertices (Corners):* How many corners does the shape have?

Side Lengths:* Are the sides all the same length, or are some sides longer than others?

Angles:* Are the angles inside the shape right angles (like the corner of a book), or are they larger or smaller?

Symmetry: Symmetry means that a shape or object looks the same on both sides if you were to fold it in half. The line where you fold the shape is called the line of symmetry (also sometimes called the axis of symmetry). Imagine drawing a line down the middle of a square. If you folded the square along that line, the two halves would match perfectly. That means the square has a line of symmetry. Some shapes have more than one line of symmetry! The square has four. Can you find them all? Shapes that do not have a line of symmetry are called asymmetrical. Examples with Calculations and Explanations: Example 1: Drawing a Square Gather your materials: You need a ruler, a pencil, and a piece of paper.

Decide on the side length: Let's say we want to draw a square with sides that are 5 cm long.

Draw the first side: Use your ruler to draw a straight line that is 5 cm long.

Draw the second side: Place the ruler at one end of the line you just drew. Make sure the ruler is at a right angle (90 degrees) to the first line. Draw another line that is 5 cm long. Why a right angle? Because a square has four right angles!

Draw the third and fourth sides: Repeat step 4, making sure the lines are at right angles to the previous lines and that they are 5 cm long. The final line should connect the two open ends.

Check: Make sure all four sides are equal and that all four angles are right angles. You have now drawn a square!

Example 2: Identifying Lines of Symmetry in a Rectangle Draw or have a rectangle: Start with a rectangle.

Imagine folding it in half: Imagine folding the rectangle along a line so that the two halves match up perfectly. Where could you fold it?

Draw the lines of symmetry: A rectangle has two lines of symmetry. One line goes down the middle lengthwise, and the other goes across the middle widthwise. Draw these lines on your rectangle. Why not more? If you try to fold a rectangle diagonally, the two halves will not match up. That's why it doesn't have diagonal lines of symmetry.

Example 3: Identifying a Symmetrical Shape Look at a picture of a butterfly. If you draw a line down the middle of the butterfly's body, you'll see that the wings on both sides are (more or less) the same. This means the butterfly is symmetrical. Now look at a picture of a random rock. If you try to draw a line down the middle, the two sides will probably look very different. That means the rock is asymmetrical. Guided Practice (With Solutions)

Question 1: What shape has three sides and three corners?

Solution: The shape is a triangle. A triangle is defined as a closed figure with three straight sides and three vertices (corners).

Question 2: Draw a rectangle that is 8 cm long and 4 cm wide.

Solution: Use a ruler to draw a line that is 8 cm long. At one end of the line, use the ruler to draw a line that is 4 cm long, making sure it forms a right angle with the first line. At the other end of the 8 cm line, draw another line that is 4 cm long, again making a right angle. Connect the tops of the two 4 cm lines with a line that is 8 cm long. You should now have a rectangle.

Question 3: How many lines of symmetry does a circle have?

Solution: A circle has an infinite number of lines of symmetry.