Flat Shapes: 2D Shapes

Shapes are all around us! Some shapes are flat — they only go across and up-down, not in-and-out. These are called 2D shapes (two-dimensional). The "2D" means they have two dimensions: length and width.

The Circle#

A circle is a perfectly round shape. It has:

• No corners (no vertices)
• No straight sides — it is one smooth curved line
• All points on the edge are the same distance from the center

Examples of circles: a coin, a wheel, a pizza, the sun, a clock face.

The Square#

A square is a shape with:

• 4 sides that are ALL the same length
• 4 corners (vertices)
• All 4 corners are right angles (like the corner of a book)

Examples of squares: a checkerboard square, a cracker, a sticky note.

The Rectangle#

A rectangle is a shape with:

• 4 sides — the opposite sides are equal in length
• 4 corners (vertices)
• All 4 corners are right angles

A square is actually a special rectangle where all four sides are equal! But most rectangles have two longer sides and two shorter sides.

Examples of rectangles: a book, a door, a window, a dollar bill.

The Triangle#

A triangle is a shape with:

• 3 sides
• 3 corners (vertices)

Triangles can look different from each other — some are tall and pointy, some are flat and wide — but they all have exactly 3 sides and 3 corners.

Examples of triangles: a yield sign, a pizza slice, a roof of a house, a musical triangle.

Comparing 2D Shapes#

Remember these differences:

• Circle: 0 sides, 0 corners (round)
• Triangle: 3 sides, 3 corners
• Square: 4 equal sides, 4 corners
• Rectangle: 4 sides (opposite sides equal), 4 corners