Shape & Space
2D Shapes: Square, Rectangle, Circle, Triangle
Junior Infants · Senior Infants · 1st Class · 2nd Class
- ✓By the end of this lesson students will be able to identify and name squares, rectangles, circles, and triangles.
- ✓By the end of this lesson students will be able to describe the key properties of squares, rectangles, circles, and triangles (number of sides, number of corners, straight or curved sides).
- ✓By the end of this lesson students will be able to sort groups of 2D shapes based on their properties.
- ✓By the end of this lesson students will be able to recognise squares, rectangles, circles, and triangles in everyday objects.
Key concepts
A 2D shape is a flat shape that you can draw on paper. It only has length and width, but no thickness.
A side is an edge of a shape. It can be straight or curved.
A corner is where two sides of a shape meet. It can also be called a vertex (plural: vertices).
A square is a 2D shape with 4 straight sides. All 4 sides are the same length. It has 4 corners.
A rectangle is a 2D shape with 4 straight sides. It has 4 corners. Its opposite sides are the same length (two long sides and two short sides, or all four sides the same length, like a square).
A circle is a 2D shape with 1 curved side. It has no corners.
A triangle is a 2D shape with 3 straight sides. It has 3 corners.
Key facts to remember
- 1A square has 4 straight sides that are all the same length, and 4 corners.
- 2A rectangle has 4 straight sides and 4 corners. Its opposite sides are the same length.
- 3A circle has 1 curved side and no corners.
- 4A triangle has 3 straight sides and 3 corners.
- 52D shapes are flat and can be drawn on paper.
- 6We can describe shapes by counting their sides and corners, and by saying if their sides are straight or curved.
- 7A square is a special type of rectangle.
Worked examples
Example 1
Look at this shape. What is its name? Tell me about its sides and corners.
Answer
This is a square. It has 4 straight, equal sides and 4 corners.
Remember, a square is a special type of rectangle where all sides are equal.
Example 2
You have a group of shapes: a square, a circle, and two triangles. Sort them into groups based on the number of straight sides.
Answer
Group 1: Square (4 straight sides). Group 2: Circle (1 curved side, no straight sides). Group 3: Two triangles (3 straight sides each).
Sorting helps us understand how shapes are alike and different.
Example 3
Look around your classroom. Can you find something that is a rectangle? Can you find something that is a circle?
Answer
The door is a rectangle. The clock is a circle.
2D shapes are all around us in the real world!
Common mistakes
- ✗Confusing a 2D shape (like a circle) with a 3D object (like a ball). A circle is flat, a ball is round and solid.
- ✗Saying a rectangle has all equal sides. Only a square (which is a type of rectangle) has all equal sides.
- ✗Not counting all the sides or corners correctly when describing a shape.
- ✗Confusing the terms 'side' and 'corner'.
- ✗Calling a square a rectangle, but not understanding that a rectangle can also be a square.
Exam tips
- ★Always count the number of sides and corners very carefully.
- ★Check if the sides are straight or curved. This is very important for circles!
- ★Practice drawing the shapes and saying their names and properties out loud.
- ★Look for 2D shapes in everyday objects to help you remember them.
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