# Silhouettes of Geometric Solids by aXx645

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Whole Class

What is a silhouette? How is it produced?

Introduce the class to the set of 12 geometric solids (see below). Name as many as you
can.

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If I place the cube on the overhead with one of the squares on the bottom, what do you
think its silhouette will look like on the screen? Draw your prediction in the space below.

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Place the cube on the screen and turn it on. Ask if everyone guessed the silhouette
correctly.

Repeat this with the narrow cylinder placed on the overhead with one of the circular
bases on the overhead surface. Have them draw the predicted silhouette in the space
below.

What do you think the silhouette of the narrow cylinder will be if you lay it on the
overhead on its curved side? Draw your prediction in the space below.

Place the narrow cylinder on overhead on its curved side and turn on the overhead.

Were you correct? Can you find any other items in the room that would have a silhouette
that is a rectangle? Explain why you think it will have a rectangle for a silhouette. We

Pair Activity: Matching Solids and Silhouettes

The next page shows silhouettes for geometric solids. Determine which of your
geometric solids would make each silhouette. (Note: Some may be slightly smaller or
larger than the actual shape.) A silhouette may match several solids or none.

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Page 74 here

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Whole Class

Many solids make more than one silhouette. Can you find a solid that will make different
silhouettes depending on where the light is positioned with respect to the solid? Describe
the solid and show the different silhouettes in the space below.

Look at Student Sheet 5 on the next page. I have arranged nine geometric solids on this
sheet of paper to match the diagram. Each team should do the same at their table. Place
your little person at the point B in the diagram. What will the silhouette of the square
prism look like to this person? Draw what you think it will look like in the space below.

Place the square prism on the overhead so the silhouette will match what a person at B
would see. Does this silhouette look like your prediction? Why or why not?

Small Group Activity

Complete Student Sheet 5 in your group. Note that your little person can be facing in any
direction at each point in the landscape. Each person on your team should agree on the
answers to the student sheet. You must convince your teammates that you are correct.
Remember that both shape and size matter. After completing Student Sheet 5, try Student
Sheets 6 through 9.

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Pages 75 – 79 here

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