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Grade 5 Math · Level 4, Solids, Volume & Data

Cross-Sections of 3D Solids

How the lesson starts: Cross-Sections of 3D Solids

1. Baker Theo's shape cakes

   This is Baker Theo's shape bakery! Theo bakes cakes shaped like balls, cans and boxes. When he makes one straight cut, a flat face appears on the cake. That flat face is called a cross-section!

2. Slice three cakes

   The ball cake is a sphere: slice it anywhere and the face is a circle. The can cake is a cylinder: cut across, parallel to its round base, and you see a circle. The box cake: cut parallel to a face, and you see a rectangle.

3. Copy the base

   Here's a handy rule. A cut parallel to the base makes a copy of the base. A cylinder's base is a circle, so the cut is a circle. A box's face is a rectangle, so the cut is a rectangle. Watch out: name the flat face, not the cake!