SLICE IT: Cross-Sections of Solids
Slice It: Cross-Sections of Solids — Interactive 7.G.A.3 Activity
Help your students master cross-sections with this hands-on, self-checking digital activity built for Common Core standard 7.G.A.3. Instead of guessing from a flat textbook picture, students slide a cutting plane through 3D solids, name the two-dimensional shape that results, and calculate its dimensions from the solid's given measurements. The cross-section reveals only when their shape and dimensions are both correct, so students get immediate feedback and stay engaged.
This activity moves students beyond simply naming shapes. They reason about why a slice produces a given cross-section and how its size relates to the original solid, connecting cross-sections to the proportional and similarity reasoning at the heart of Grade 7.
What's included:
- Three rectangular prism problems covering horizontal and vertical slices, showing how the same box yields different rectangles depending on orientation
- Three square pyramid problems including horizontal slices (similar, scaled-down shapes), a vertical slice through the apex (triangle), and a slice beside the apex (trapezoid)
- Three curved-solid extension problems (cylinder, cone, sphere) to stretch curious students beyond the standard
- Interactive move-the-plane slider so students explore multiple slice positions before committing
- Self-checking answer reveal that shows the true cross-section only when the response is correct
- No-prep and paperless — ready to assign as-is
Skills students practice:
- Identifying cross-sections of right rectangular prisms and pyramids
- Understanding how slice orientation changes the resulting shape
- Computing cross-section dimensions using congruence and similarity
- Visualizing 3D-to-2D relationships and spatial reasoning
Perfect for: in-class practice, math centers, homework, sub plans, early finishers, or test review on cross-sections and geometry.
Standard alignment: CCSS 7.G.A.3 — Describe the two-dimensional figures that result from slicing three-dimensional figures.
Grade level: 7th grade math (also useful as review or enrichment for 8th grade geometry)
Learning Objective
Students describe the two-dimensional cross-section that results when a plane slices a right rectangular prism or right rectangular pyramid (7.G.A.3). For each slice they name the shape and compute its dimensions from the solid's measurements, reasoning that a slice parallel to a face is congruent to that face (prism), and that a slice parallel to the base is a similar, scaled-down copy (pyramid). By the end, students can predict how a cross-section's shape and size change as the slicing plane's position and orientation change.
