Unit 7, Lesson 11
Slicing Solids
Grade 7
Preparation
Lesson Narrative
This lesson introduces the idea that slicing a three-dimensional figure with a plane results in a two-dimensional cross-section. Slicing a fruit or vegetable, dipping the exposed face in paint, and stamping it on a paper helps students make sense of the two-dimensional face that is created by the slice (MP1). Given two-dimensional representations of how objects are sliced, students practice visualizing the three-dimensional figures and the resulting cross-sections.
- Categorize images of planes intersecting pyramids and prisms, and describe (orally) the categories.
- Comprehend that the term “cross-section” (in spoken and written language) refers to the two-dimensional face that results from slicing a three-dimensional figure.
- Describe, compare, and contrast (orally and in writing) different cross-sections that could result from slicing the same pyramid or prism.
Let's see what shapes you get when you slice a three-dimensional object.
Required Materials
Activity 2
Required Preparation
As part of the activity, the teacher will slice a fruit or vegetable to show a cross-section. Recommended are apples, potatoes, or carrots. Tempera or acrylic paint can also be used to stamp the cross-section onto paper.
For the digital version of the activity, acquire devices that can run the applet.
A base is a specific face of a prism or pyramid.
A prism has 2 identical bases that are parallel. A pyramid has 1 base.
A prism or pyramid is named for the shape of its base.
A cross-section is the new face that is seen when a three-dimensional figure is sliced.
A rectangular pyramid is sliced parallel to the base. The cross-section is a smaller rectangle.