Investigating Volume 3:

# Does changing the shape of an object change its volume?

## 4. Make meaning

All Class 10 Mins

### Purpose of the discussion

This class built 10 cubic centimeter shapes.

This discussion will bring forward students’ ideas about volume. When 8 cubic centimeters of plastic modeling clasy are reshaped, does the volume stay the same or change? You may want to review The Challenges of Learning About Volume. It’s easy to underestimate the challenges presented as students begin to learn about volume. In this discussion, listen carefully to students’ ideas. Provide plenty of “wait time” so you and your students can make sense of the conversation. In this discussion, encourage students to support their position (no, the volume doesn’t change or yes, it does) with evidence and reasoning.

Deep understanding of volume develops over time. If a student’s understanding of volume seems fragile at this point in time, remember that this concept will be revisited and is a focus of the 4th grade curriculum.

### Revisit the activities the students have just completed

Remind students where they began: making different arrangements with their 8 centimeter cubes and deciding that the volume was always 8 cubic centimeters — they hadn’t added any cubes or taken any away. Then they made their own centimeter cubes out of plastic modeling clay, put them together, changed the shape of some of them, and wondered if the volume was the same or different.

### Engage students in the focus question

Does changing the shape change the volume?

• The volume has to be the same because we haven't added any plastic modeling clay or taken any away.
• If we turned the plastic modeling clay back into centimeter cubes, there would be 8 of them so the volume hasn't changed.
• I made 4 of the cubes into a ball and my object looks bigger now so there is more volume.

### Supporting questions

• If you took the plastic modeling clay in your rabbit (new shape) and reshaped it back into cubes, what do you think you would find?
• What was the volume of your original 8 plastic modeling clay centimeter cubes?
• Did you add any plastic modeling clay to your original 8 cubic centimeters or take any away?

### Recap the discussion

Summarize the idea that volume is the amount of space an object takes up. As long as we don’t add any material or take any away, the volume will stay the same even if we change the shape of the object.