students in a class discussion about their knowledge of surface area,
making certain they understand surface area is the two dimensional
measurement of a three-dimensional figure. Use several different
rectangular prisms for students to demonstrate their understanding of
- How do you find area of a rectangle?
- How many rectangular faces make up a rectangular prism?
- Although each face of the rectangular prism is two-dimensional, together what do they make?
- What is the sum of the areas of the faces on a rectangular prism called?
- Why are square units used when measuring surface area?
- In your own words, give a definition of
surface area of a rectangular prism?
Go on-line to the Side Length, Volume, and Surface Area of Similar Solids Applet.
When the applet opens, students should click on "Measures" under the 3D mode.
There are two similar rectangular prisms, one purple and one red. The
red prism remains the same. The length is 20 units, the width is 10
units, and height is 7 units. Students should use the slide bar or the
red dot to change the size of the purple rectangular prism.
Next students should change the size of the purple prism and
observe the change in the ratio of L : 1 (scale factor). Note how the
Surface Area of Prism A and Prism B and their ratio change for
different length measures.
Using the Rectangular Prisms table on the Purple Prisms activity sheet, students should record the Surface Area of A, the
Surface Area of B, the ratio of Surface Area A : B, and the scale factor L : 1 for ten different rectangular prisms.
Ask students the following questions as they complete the activity:
- Why is Surface Area B always 8.93 square units?
- How do you know what the width and height of A are?
- Are these prisms similar? How do you know?
- Which column from the Student Learning Guide represents scale factor? Why?
Students should now look at the L : 1 and Surface Area A : B ratio on the table. Click on Show Surface Area graph. Use the Questions for Students (below) to conclude the lesson.