In Grade 4 Curriculum:

2. Heavy for Size:  Investigation 2.1

Same volume, same weight?

3. Make meaning

Discussion 15 Mins

Classroom Case 2

Screenshot from Grade 4 Classroom Case 2

Discussing Data

The Role of a Data Discussion

Available online at inquiryproject.terc.edu

There are two layers of data to grapple with in this discussion:
(1) establishing a single weight for each of the four samples, since it's unlikely that all groups found identical weights for a sample;
(2) once the weight of a 40cc sample is established for each material, using the data to address the investigation question: Same volume, same weight?

Purpose of the discussion

The purpose of the discussion is for students to

  1. connect the investigation question and their data.
  2. wrestle with discrepant data.
  3. make claims and describe the supporting evidence.
  4. suggest explanations.

Again, the discussion focuses on the investigation question.

Engage students in the focus question

Remind students that the purpose of collecting the weight data was to answer the investigation question:

Same volume, same weight? If samples of different materials have the same volume, do they have the same weight?

Do we have data that we can use to answer this question?

As you listen to student responses, check to be sure everyone knows what information is contained in each of the three columns in the class data table. The class table is a simplified version of the one in their notebooks.

How can we reconcile discrepancies in the data?

Not all groups found the same weight for 40cc of water (oil, sand, organic soil). Why do you think that is and what number should we use for the weight?

Listen to students‘ ideas about why their weight measurements vary and how they can decide on a "class" value for the weight of 40cc of water.

Some possible student ideas

Explanations for small differences

  • There may be tiny differences in the amount of sand (water, oil, organic soil) in the containers.
  • There may be tiny differences between the scales.
  • The scales round the actual weight to the nearest gram, so tiny differences in actual weight can appear to be larger on the scales.

Explanations for large discrepancies

  • We forgot to include the weight of the container cap.
  • We made a subtraction error.

Strategies for coming up with a weight the class can agree on

  • Use the weight that appears most often.
  • Pick a round number that seems an appropriate middle point.
  • Make a new 40cc sample and weigh it.

Once a typical weight for each material has been established, ask someone to make up a sentence that describes the data in each row of the table. For example:

The top row tells us that a forty cubic centimeter sample of water weighs forty grams.

What claims can we make and what is the supporting evidence (data)?

Now that the data has been "cleaned up", ask:

  • Let's return to the investigation question: Same volume, same weight? If samples of different materials have the same volume, do they have the same weight?
What claims can you make, and what evidence can you point to that supports the claims?

The cleaned-up data should be clear:  equal volumes of different materials can have different weights. Encourage students to describe the data they use as evidence for a claim.

What is a possible explanation?

Ask the group to explain why they think same-sized samples of earth materials have different weights.

  • What might be a possible explanation for why, when the volumes are the same, the weights of different materials are different?

Listen to students‘ ideas. If they don't suggest that each kind of material has its own properties, you might remind them of their prior experience with properties of materials. In addition to properties such as color or texture, materials can have different weights even when they have the same volume (take up the same amount of 3-D space). We call this property "heavy for size". The sand is heavy for its size compared with the same volume of water, mineral oil, or organic soil.

Summarize the discussion and recap the investigation

Here is what I think I heard you say about the data we collected...

In your summary, include the two main parts of the data discussion (1) ideas about how to explain the fact that different groups got different results and how to come up with a single weight, and (2) once they have a single weight for 40cc of each material, ideas about how to answer the investigation question.

Here are some of the things we discussed and explored today:

  • Volume is the amount of 3-D space an object takes up.
  • We measured the weights of equal volumes of sand, organic soil, water, and oil.
  • We think we got slightly different weights for each type of material because we used different scales and there may be small differences between the scales.
  • Even though we got slightly different measurements, we agreed that 40cc's of water weigh 40g, etc. (read the values from the table).
  • We answered the investigation question using the data we collected: equal volumes of different materials do not have the same weights. So some materials are heavier for their size than other materials.

Save the class data chart for Investigation 2.4.