2D & 3D Objects: Properties & Relationships

Instructor: Yuanxin (Amy) Yang Alcocer

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

Read this lesson to learn about the similarities and differences between a two-dimensional object such as a drawing on a sheet of paper and a three-dimensional object such as a basketball.

2D Objects: Properties

Did you know that when you draw on a piece of paper you are drawing something called a two-dimensional object? A two-dimensional (2D) object is an object that only has two dimensions, such as a length and a width, but no thickness. Draw a square on a piece of paper and you have a two-dimensional square. Draw a circle on a piece of paper and you have a two-dimensional circle. Draw a stick person and you have a two-dimensional stick person. A dimension is something that can be measured like your length, your width, and your height.

2D objects drawn on a sheet of paper
2d 3d objects

Do you see anything that all your two-dimensional objects share? They all share two dimensions. They all have a length and a width. Certain shapes have specific defining measurements, such as the radius of circles. But none of them have thickness to them. You can describe all these shapes using just two dimensions. For example, the stick person can be said to be so many inches tall and so many inches across. Only two dimensions are mentioned.

You can easily tell when you are looking at a two-dimensional object. The one thing you look for is whether the object is flat. If it's completely flat, meaning it doesn't have any thickness to it, then it is two-dimensional. Because your paper is flat, everything you draw on it is two-dimensional.

Is your paper two-dimensional, though? It looks two-dimensional since it's so thin that it seems to only have two dimensions, but in reality, it's a three-dimensional object.

3D Objects: Properties

A three-dimensional (3D) object is an object with three dimensions: a length, a width, and a height. You can hold 3D objects in your hand and you can turn them around. This is what makes a piece of paper a three-dimensional object. It has a thickness, even if that thickness is very small. It's not a 2D object because it has thickness.

The world you live in is a three-dimensional world, so everything you see around you- your house, your computer, your car, your phone- are all 3D objects. All these objects can be described in three dimensions. For example, you can describe your phone by saying that it is so many inches wide and so many inches long and so many inches high. It has three dimensions.

Relationship Between 2D and 3D Objects

Two-dimensional objects are related to three-dimensional objects in that you can see 2D flat shapes on the faces of 3D objects. The face of a 3D object is a flat side of the object. For example, the bottom of a soda can is one of its faces. You can see that the shape of the soda can's bottom is a circle, a 2D object. If you dipped the bottom of your soda can in ink and then touched a piece of paper with it, the can would leave a circle on the paper.

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