Lesson 7 of 11
The job picks the faces
Show on a big screenAn object has many faces. The question decides which ones count.
Step 1 of 4
- One object; a job picks how to read it.
- The question's words choose a branch.
- Covering reads the outside faces.
- Filling takes the whole inside.
Faces for the job
A job is what the question asks for, such as painting. Paint reaches only the outside. So parts that touch are left out.
| Object | Job | Faces counted |
|---|---|---|
| Tent | Canvas | Cone skin + cylinder wall |
| Round-bottomed toy | Paint | Cone skin + dome skin |
| Capsule | Paint | 2 domes + cylinder wall |
| Cube with a bowl | Surface | 6 faces − mouth + bowl |
| Cylinder with a bowl of its own radius at each end | Surface | Wall + 2 bowls |
In the last row, the two bowls replace both end discs. Only the wall and two bowls remain.
Example: a capsule has radius 7 and a cylinder 10 long. So r = 7 and h = 10. The wall is 2πrh = 2 × 22/7 × 7 × 10 = 440. Each dome is 2πr² = 2 × 22/7 × 49 = 308. Two domes make 2 × 308 = 616. The surface is 440 + 616 = 1056.
Read the job before the shapes. List the faces you can touch or see. Leave out parts that touch each other. Leave out parts the job skips.
Pick the faces for five jobs.
Loading lab…
Try the lab to finish this lesson.