In seventh grade, we explore three-dimensional geometry, including finding the surface area of prisms and spheres. We also find the volume of many different kinds of prisms. Finally, we examine cross-sections of these solids.
Prisms
A prism is a three dimensional shape that “grows” from a two-dimensional base.
Prisms have:
- No curved edges
- Two parallel bases
- Side faces that are parallelograms
- Click here for more information on the properties of prisms.
Surface Area
We joke that when dealing with surface area, it’s what’s on the outside that counts! To find surface area, find the sum of the area of all the bases and faces of the solid figure.
When finding the surface area of a sphere, students use the formula, 
Click here to watch a video on finding surface area of a prism, and here to watch a video on finding surface area of a sphere. Click here to practice finding surface area for yourself!
Volume
When we work with volume, we return to the adage “it’s what’s inside that counts!” To find the volume of a prism, we find the area of the base of the prism, and multiply it by the height.
Click here to watch a video about finding the volume of a prism, and here to try some practice problems.
Cross Sections
Time to slice and dice! When taking cross-sections of 3-D objects, we take a horizontal or vertical slice of the solid. The two-dimensional result is called a cross-section.
Click here to watch a video on cross-sections of a 3-D figure, and here to try some practice problems. Happy slicing!
Mrs. Jette Math 7A Blog.2017.18 