1The three parts of a rectangular prism
A rectangular prism is made up of flat faces, straight edges where two faces meet, and pointed vertices where three edges meet.
6faces
12edges
8vertices
2Opposite faces are always the same size
A rectangular prism has three pairs of opposite faces: top-bottom, front-back, and side-side. Looking from one direction, you only see 3 faces, but there's a matching, same-size face on the opposite side of each one — 6 faces in total.
3A cube is a special rectangular prism
A rectangular prism whose length, width, and height are all equal is called a cube. A cube still has 6 faces, 12 edges, and 8 vertices — what makes it special is that all six of those faces are congruent squares.
4You can count parts even when you can't see them
There's a trick for finding the hidden parts.
Any face, edge, or vertex you can't see from the front exists in exactly the same way on the far side. Add the number you can see from the front to the number that's hidden, and you get the exact total.
Any face, edge, or vertex you can't see from the front exists in exactly the same way on the far side. Add the number you can see from the front to the number that's hidden, and you get the exact total.
Solid lines are edges you can see, dashed lines are edges hidden behind — add them together and you get 12
5Try this
- Press the face, edge, and vertex buttons one at a time. Check where the dashed, hidden parts show up.
- Adjust it into a cube. Check whether the face, edge, and vertex counts stay the same once length, width, and height all match.
- Check it with a real box. Pick up a shipping box or tissue box at home and trace the faces, edges, and vertices with your finger.