# Take Apart 3D Shapes

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## Objective

SWBAT identify three-dimensional shapes used to build a composite shape using the strategy act it out.

#### Big Idea

If you build it, they will come ... What could be more fun than building bridges and castles in math class? In this lesson students analyze a composite shape to determine the individual 3D shapes that were used to make the composite shape.

## Activating Strategy

10 minutes

I start this lesson by reading the book, “Three Dimensional Shapes: Cubes”.  I like to use this book because it demonstrates the various real life uses for 3D shapes.  There are four books in the series: cones, cubes, spheres and cylinders.  All of the books show real life 3D objects that are seen in our everyday lives.

I then hand out a set of 3D shapes to students, or pairs of students and instruct them to build a castle at their tables.  I don't want the activity to get out of hand, so I give them about 3 minutes.  After the castles are built, we do a quick gallery walk and explore and analyze the castles that were built.  Students line up in line order and follow the leader (me) in a snake around the room.  I call on a few volunteers to share their castle and discuss the shapes that were used.

In the standard, 1.GA.2, children analyze a composite shape to determine the individual shapes of which it is made. I have found that some children may immediately visualize which shapes are used in the composite shape and resist modeling the composite shape with three-dimensional shapes. "I can see in my head the blocks used in the bridge!" is a possible response from children who can mentally take apart shapes. While it's great that they feel so confident, I still insist that children adept at visualization should use blocks to verify what they visualize. This will help solidify their understanding and help them check themselves for errors.

Here are some ways you might encourage them:

• Show me how you would build this bridge using real blocks.
• How would you instruct someone to copy this bridge?

## Teaching Strategies

15 minutes

Then, displaying the first slide on the Take apart 3D.ppt, I have children look at the bridge pictured on the slide and read the following question aloud to the class.

Mike has cones, cubes, cylinders, and rectangular prisms. He chose some shapes to build a bridge. Which shapes did Mike use to build the bridge?

I guide the discussion:

• Look at Mike’s bridge. How many blocks did he use? (7)
• How many different shapes did he use? (2)
• What shapes are they? (cylinders and rectangular prisms)

If shapes are available, I allow students to build the same bridge.

• How can you check that your bridge is just like the one in the picture? (I count the number of rectangular prisms in the picture and in my bridge. The numbers should match. I do the same for the cylinders. I also check the positions of the shapes in both bridges.)

For the standard, 1.G.A2, some students may have difficulty visualizing how to combine the smaller shapes into larger shapes.  To help them visualize the combination, I start with making a shape myself, and having the student select the two shapes that I used and copy the new shape.  We then discuss how the shapes that we used are still within the new larger shape that we created.  I repeat the activity.  By allowing the student to select the appropriate shapes that I used, they will begin to visualize the smaller shapes that were used to make the larger shape.

## Independent Practice

30 minutes

I have students complete a Take apart 3D shapes_worksheet.docx for the independent practice portion of this lesson.  I hand out the worksheet, and display the second slide of the PowerPoint.  I use the questions below to guide children through the first problem.

• What do you need to find in question 1? (the shapes Kim uses to build the tower)
• How many shapes did Kim use to build the tower? (2)
• How could you describe the shapes she used?  (She used a green cone on top of a red cylinder.)
• Look at the cylinder in the tower and the cylinder in the answer choices. Does it matter that they do not look the same? Explain. (no; I am choosing the shapes that are used to build the bridge, not the actual blocks that were used.)

## Closing/Summarizing

5 minutes

To close out this lesson, I have students share their drawing for question 7 (from the worksheet) with a partner.  I instruct their partner to try to re-create the tower based on the drawing.  This is a great way for students to practice MP3.  This allows for students to use their mathematical language to assist their partner with building their tower.