# Three-Dimensional Solids

**Three-dimensional Solids** have dimensions in 3 directions - length, width and depth. In geometry, we are mainly interested in three types of 3D solids which are:

**Prism** - where the *cross-section has the same shape and the same size* all the way along the object (e.g. cube, rectangular box, cylinder)
**Pyramid** - where the cross-section has the same shape, but the *cross-section reduces in size to a point* (e.g. Egyptian pyramid, cone)
**Sphere** - round object (e.g. basketball).

## Prisms

Cube (Square-based prism) | |

Rectangular Prism | |

Triangular Prism | |

Cylinder (Circle-based Prism) | |

## Question - Prisms in Gym Equipment

Look at the gym equipment. Identify 3 prisms.

## Did You Know That...?

This triangular **prism** is dispersing white light into the seven light wavelengths of the **visible light spectrum** - red, orange, yellow, green, blue, indigo
and violet. What we cannot see with our human eyes is the **invisible light** including radio waves, microwaves, infra-red, ultra-violet, x-rays and gamma-rays.

## Pyramids

Square-based pyramid | |

Tetrahedron (Triangle-based pyramid) | |

Cone (Circle-based pyramid) | |

## Did You Know That...?

Use a magnifying glass to look very closely at the salt in your kitchen. The crystals of **table salt** (also known as sodium chloride and halite) are in the shapes of cubes.