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What are 2D Shapes? - Definition, Lesson & Quiz

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Taught by

Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught Math at a public charter high school.

In this lesson, you will find out how a flat piece of paper will help you determine what shapes are considered 2D. You will also learn the wide variety of 2D shapes you may encounter in life.

Definition

'2D' stands for 2-dimensional. A 2D shape is any shape that has two dimensions. Think about what it means to have two dimensions for a moment. If we had only one dimension to work with, we could only move backwards or forwards in a line. A line is one-dimensional. If we had two dimensions, on the other hand, we could go forwards and backwards in a line and turn in any direction to start a new line. We are essentially able to travel anywhere on a flat surface. In mathematics, a flat surface is called a plane. A plane is one example of a two-dimensional shape. A plane is essentially the largest sheet of paper you will ever find. In fact, it is a sheet of paper so large that it never ends. One way of thinking about 2D shapes is anything that lays flat on a piece of paper.

A 2D shape is any shape that can lay flat on a piece of paper
2d shapes

Take out a piece of paper, and place it on your desk. Notice how flat it is. Now take any nearby object, place it on your piece of paper, and trace around it. Look at your shape. What does it look like? Congratulations, you have just drawn a 2D shape! This is another way you can think of 2D shapes: 2D shapes are any shape you can trace from an object on a flat piece of paper.

Take a cube and trace it on a piece of paper and you will get a square shape. Take a soda can and trace it on a piece of paper. Depending on how you lay the soda can down, you will get either a circle or a rectangle. Try it out and see for yourself.

Tracing a spool right side up produces circles
spool circle

Tracing a spool on its side produces rectangles
spool rectangle

Examples of 2D Shapes

You can find 2D shapes pretty much everywhere you look. Remember back when you drew your first house. Do you remember the shapes you used to make your house? Yes, most likely you used a square for the house and a triangle for the roof. Add in a few rectangles and you have your door, windows, and a chimney. The shapes you used to draw your first house (your square, triangle, and rectangle) are all examples of 2D shapes. Why? Because all these shapes can be laid flat on a piece of paper. These are shapes you can trace from other objects as well. Look around you and you will see all these shapes around you in the real world as well.

In the world of mathematics, the list of 2D shapes is large because there is a name for practically any shape you can imagine. You have your typical squares, rectangles, and circles. You also have hexagons, pentagons, and octagons. Stars, hearts, and crescent shapes are all 2D shapes too.

Challenge yourself and see how many flat shapes you can find. Write them down and challenge yourself again in a different location to see if you can find even more.

Here is a partial list of 2D shapes'

2D Shapes
Square
Rectangle
Triangle
Circle
Clover
Diamond
Heart
Pentagon
Hexagon
Septagon
Octagon
Nonagon
Decagon
Star
Crescent
Oval
Parallelogram
Trapezoid

Summary

2D shapes can be summarized by calling them flat shapes. Any shape that can be laid flat on a piece of paper or any mathematical plane is a 2D shape. As a child, your first drawings probably used basic shapes such as squares, triangles, and circles. Now you can find 2D shapes in the world all around you. Examples of 2D shapes include rectangles, octagons, and even hearts.

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