Flat shapes
A two-dimensional (2D) shape is flat. You can draw it on paper, but you can’t pick it up or hold it like a ball. It has length and width, but no thickness.
Parts of a shape
- A side is a straight edge of the shape.
- A vertex is a corner where two sides meet. Two or more corners are called vertices.
Counting sides and vertices helps you name a shape.
Common 2D shapes
| Shape | Sides | Vertices | Looks like |
|---|---|---|---|
| Circle | 0 (one curved edge) | 0 | a plate, a clock |
| Triangle | 3 | 3 | a slice of pizza, a yield sign |
| Square | 4 equal | 4 | a window pane, a cracker |
| Rectangle | 4 | 4 | a door, a book |
| Pentagon | 5 | 5 | a home plate in baseball |
| Hexagon | 6 | 6 | a honeycomb cell |
| Oval | 0 | 0 | an egg shape |
Squares and rectangles
A rectangle has 4 sides and 4 square corners. Its opposite sides are the same length. A square is a special rectangle: all 4 sides are the same length.
So every square is a rectangle, but not every rectangle is a square.
Shapes can turn
A triangle is still a triangle if it’s upside down or tipped over. Turning a shape doesn’t change what it is. A square turned on its corner (sometimes called a "diamond") is still a square.
Shape hunt
2D shapes are hiding everywhere:
- Clock face → circle
- Stop sign → octagon (8 sides)
- Book cover → rectangle
- Sandwich cut corner to corner → two triangles
Worked examples
Example 1: A shape has 3 sides and 3 vertices. What is it?
A triangle.
Example 2: How many vertices does a rectangle have?
4.
Example 3: A shape has no sides and no vertices and is perfectly round. Name it.
A circle.
Common mistakes
- Thinking a turned square is a different shape. It’s still a square.
- Calling every three-sided shape a "pointy" triangle only. Triangles can be tall, wide or tilted.
- Counting the same vertex twice. Mark each corner as you count.
Try it yourself
- How many sides does a hexagon have?
- Name a shape with 4 equal sides.
- Which shape has no vertices?
- Is every square a rectangle?
Answers: 1) 6 2) square 3) circle (or oval) 4) yes
Quick recap
- Two-dimensional shapes are flat.
- Count sides and vertices to name them.
- A square is a special rectangle; turning a shape doesn’t change its name.