Plane Shapes, Symmetry and Cardinal Points for Primary 4

Plane Shapes, Symmetry and Cardinal Points

Performance Objectives

By the end of the lesson, students should be able to:

1. identify symmetrical plane shapes;
2. locate line(s) of symmetry of objects in the environment;
3. distinguish between horizontal and vertical lines;
4. locate the four cardinal points.

What Are Plane Shapes?

A plane shape is a flat shape that can be drawn on a flat surface. These shapes have only two measurements: length and width. They do not have thickness.

Examples of plane shapes include squares, rectangles, triangles, circles, and kites. These shapes are all around us, in the objects we see every day.

Understanding Symmetry

Symmetry is a special property that some shapes and objects have. A shape has symmetry if one half of it is a perfect mirror image of the other half.

Line of Symmetry

A line of symmetry is an imaginary line that divides a shape or an object into two identical halves. If you fold the shape along this line, both halves will match up perfectly.

Some shapes have one line of symmetry, some have many, and some have none at all.

Symmetry in Different Plane Shapes

Let us look at the symmetry of some common plane shapes:

1. Square: A square has four equal sides and four equal angles. It has four lines of symmetry. These lines pass through the middle of opposite sides and through opposite corners (diagonals).
2. Rectangle: A rectangle has two pairs of equal sides and four equal angles. It has two lines of symmetry. These lines pass through the middle of its opposite sides.
3. Equilateral Triangle: An equilateral triangle has three equal sides and three equal angles. It has three lines of symmetry. Each line passes from a corner to the middle of the opposite side.
4. Isosceles Triangle: An isosceles triangle has two equal sides and two equal angles. It has one line of symmetry. This line passes from the corner between the two equal sides to the middle of the opposite side.
5. Rhombus: A rhombus has four equal sides, but its angles are not all equal. It has two lines of symmetry. These lines are its diagonals, connecting opposite corners.
6. Trapezium: A trapezium is a four-sided shape with only one pair of parallel sides. Most trapeziums do not have any lines of symmetry. However, a special type called an isosceles trapezium can have one line of symmetry. For general trapeziums, we consider them non-symmetrical.
7. Parallelogram: A parallelogram is a four-sided shape with two pairs of parallel sides. A parallelogram does not have any lines of symmetry.
8. Kite: A kite is a four-sided shape with two pairs of equal-length sides that are next to each other. It has one line of symmetry. This line is one of its diagonals, which connects the corners where the unequal sides meet.
9. Circle: A circle is a perfectly round shape. It has an infinite number of lines of symmetry. Any line that passes through the centre of a circle is a line of symmetry.

Locating Lines of Symmetry in Objects

Many objects in our environment also have lines of symmetry. Identifying these lines helps us understand the balance and design of objects.

Examples of objects with lines of symmetry include:

1. Leaves: Many leaves have one line of symmetry down their middle.
2. Butterflies: A butterfly has one line of symmetry down the middle of its body.
3. Chairs: Many chairs have one line of symmetry down the middle.
4. Doors and Windows: Rectangular doors and windows often have two lines of symmetry.
5. Cars: A car, when viewed from the front or back, often has one line of symmetry down its middle.

To locate a line of symmetry, imagine folding the object. If the two halves match perfectly, the fold line is a line of symmetry.

Horizontal and Vertical Lines

Lines can be in different positions. We often talk about horizontal and vertical lines.

Horizontal Lines

A horizontal line is a straight line that goes across from left to right, like the horizon where the sky meets the land. It is flat or level.

Vertical Lines

A vertical line is a straight line that goes straight up and down, like a tall wall or a standing pole. It is upright.

Distinguishing Between Horizontal and Vertical Lines

It is important to be able to tell the difference between these two types of lines. Look around your classroom or home for examples:

1. Tabletop: The top edge of a table is a horizontal line. The legs of the table are vertical lines.
2. Wall: The bottom and top edges of a wall are horizontal lines. The side edges of a wall are vertical lines.
3. Door: The top and bottom frames of a door are horizontal lines. The side frames of a door are vertical lines.
4. Electric Pole: An electric pole standing upright is a vertical line. The wires stretched between poles are horizontal lines.
5. Bookshelf: The shelves are horizontal lines, and the sides that hold the shelves are vertical lines.

Cardinal Points

Cardinal points are the four main directions used to find locations and give directions. They are North, South, East, and West.

The Four Cardinal Points

1. North (N): This is usually the direction towards the top of a map. It is opposite to South.
2. South (S): This is the direction opposite to North, usually towards the bottom of a map.
3. East (E): This is the direction where the sun rises in the morning. It is opposite to West.
4. West (W): This is the direction where the sun sets in the evening. It is opposite to East.

Locating the Four Cardinal Points

You can use the sun to help you find the cardinal points:

1. Find East: Stand facing the direction where the sun rises in the morning. This direction is East.
2. Find West: Once you are facing East, your back will be towards the West, where the sun sets.
3. Find North: If you are facing East, your left hand will point towards North.
4. Find South: If you are facing East, your right hand will point towards South.

Knowing the cardinal points helps people navigate, read maps, and understand directions in their environment.