A 3-D solid (sometimes called a 3-D shape) is a figure that is not flat, it is three-dimensional. Some examples of 3-D solids include a cube, rectangular prism, cone, cylinder, pyramid, sphere and so on. Once your child has had an opportunity to explore various 3-D solids, she will be ready to begin looking at the main components of 3-D solids: faces, edges and vertices.

Faces

A face is a flat surface on a 3-D solid. Students are often asked to identify the number of faces on 3-D solids. It is important to note that a face must be flat, so a sphere technically does not have a face, it has a curved surface. Another noteworthy point: Your child may also learn about a *base*. A base is a special kind of face. Cylinders and prisms actually have two bases that are both parallel and congruent.

Edges

An edge is a line segment where two faces meet. To help my students better understand edges, I ask them to run their finger along the edge of a tissue box. Try challenging your child to try to find all the edges on a box. Identifying the edges of 3-D solids is typically more difficult for students.

Vertices

“Vertices” is the plural of one vertex. Vertices are corner points. Vertices are found where edges meet.

Here is a chart with the numbers of faces, edges and vertices of some common 3-D solids. Please note that your child may not learn all of these solids at one time.

3-D Solid | FACES | EDGES | VERTICES |

CUBE | 6 | 12 | 8 |

RECTANGULAR PRISM | 6 | 12 | 8 |

CYLINDER | 2 | 0 | 0 |

CONE | 1 | 0 | 0 |

SQUARE PYRAMID | 5 | 8 | 5 |

TRIANGULAR PRISM | 5 | 9 | 6 |

SPHERE | 0 | 0 | 0 |

TRIANGULAR PYRAMID (TETRAHEDRON) | 4 | 6 | 4 |

HEXAGONAL PRISM | 8 | 18 | 12 |

What to Watch For:

- Children often confuse 3-D solids (sometimes called 3-D shapes) with 2-D shapes. They often learn about shapes (square, rectangle, triangle, pentagon, hexagon, octagon, rhombus, trapezoid, etc…) at the same time as 3-D solids, which can also be confusing. Be sure your child understand the concept that 3-D solids have 3 dimensions. You will likely need to explain what 3-dimensional means (length, width, and height).

WANT MORE?

- As always, playing math games at home is a great way to reinforce math skills learned in school.
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