Lesson 6

The purpose of this warm-up is to elicit the idea that weight can be measured. While students may notice and wonder many things about this image, how weight can be measured is the important discussion point.

• Groups of 2
• Display the image.
• “What do you notice? What do you wonder?”
• 1 minute: quiet think time

• “Discuss your thinking with your partner.”
• 1 minute: partner discussion
• Share and record responses.

• “Today we’ll begin learning about weight. Weight is how heavy an object is. When are some times that we think about weight?” (When buying fruit or vegetables at the store. When getting a check-up at the doctor’s office.)
• “How could weight be used to decide how much a piece of fruit should cost?” (The more the fruit weighs, the more it’s going to cost because we’re getting more.)

The purpose of this activity is for students to learn that grams and kilograms are standard units for measuring weight. Students are introduced to the units using common objects as benchmarks. For each benchmark, students hold an object of some number of grams or kilograms and think of an example of an object that has about the same weight. Then, students look for items in the room that are in specific weight ranges. 

If time permits and if a scale or a balance is available, give students an opportunity during the synthesis to confirm the weights of the objects they estimated. Depending on the number of weight measurement tools available, arrange for a whole-class weighing demonstration with the objects students chose, or arrange for students to weigh their chosen objects in groups, taking turns with each type of available tool.

• Create a set of metric weights (1 kilogram, 2 kilograms, 1 gram, 10 grams, 100 grams). Weights can be made by filling bags with the following quantities of objects:
  • for 1 kilogram: 1,000 jumbo paper clips or a 1 liter bottle filled with water
  • for 1 gram: 1 large paper clip
• Create a poster with the labels “less than 1 gram,” “between 1 gram and 100 grams,” “between 100 grams and 1 kilogram,” and “over 1 kilogram” for the synthesis.
• If possible, gather scales (analog and digital), primary balances, and any other available weight measurement tools for the synthesis of Estimate Weight activity. Prepare enough tools for each group of students to have one, or prepare one for a whole-class weighing demonstration.

• 5 groups
• “Grams and kilograms are some units we use to measure weight. A gram is a small metric unit of weight and is about the same weight as a paper clip. A kilogram is a larger metric unit of weight and is about the same weight as a basket of apples.”

• “We are going to hold some weights and get a sense of how heavy 1 gram, 10 grams, 100 grams, 1 kilogram, and 2 kilograms are.”
• “Your group will have 2 minutes with each weight. In that time, everyone in your group should hold the weight and list some things you think weigh about the same. You can share ideas with your group as you write.”
• Distribute objects with the following weights, one object for each group:
  • 1 gram
  • 10 grams
  • 100 grams
  • 1 kilogram
  • 2 kilograms
• 2 minutes: small-group work time
• Rotate materials.
• 8–10 minutes: Repeat rounds of 2 minutes with each weight until each group has had every weight.
• Monitor for examples of each weight that students generate.
• Pause for a discussion.
• Invite students to share 1–2 examples for each measurement. Have students add the examples that are shared to their list.
• “Now, look at the table in the second problem. Work with your group to find objects around the room that belong in each column based on their weight.”
• 5–7 minutes: small-group work time

If students say they aren’t sure in which column an object belongs, consider asking:

• “How would you describe the weight of the object compared to a gram or kilogram?”
• “How many grams or kilograms do you think it weighs?”

• Select students to share 1–2 examples from each column.
• Record responses on the poster labeled with the different categories.
• If possible, allow students to use a scale or a balance to confirm the weight of some of their objects.
• To familiarize students with the available weight measurement tools, display them for all to see, and consider asking:
  • “What do you notice? What do you wonder?”
  • “How do we read the scale? What if the scale is in between two numbers?”
  • “How do we know when a balance shows that objects have the same weight?”
•  If multiple scales are available, allow students to weigh their objects in groups. If only one scale is available, demonstrate it for the class.

The purpose of this activity is for students to use what they’ve learned about grams and kilograms to estimate the weights of some common pets. Students should rely on the experiences they have had in previous activities to explain why the estimates they choose are reasonable. In the synthesis, students consider when it might be helpful to estimate a weight rather than measure the exact weight.

• Groups of 2

• “Work with your partner to match each pet with an amount that could be its weight.”
• 3–5 minutes: partner work time
• Monitor for students who refer back to the activities where they felt different weights to determine a reasonable estimate of each pet’s weight.

If students choose estimates for the weight of the pets that aren’t reasonable, consider asking:

• “Tell me how you estimated the weight of the pet.”
• “Would the pet weigh more or less than a gram (or kilogram)?”

• Invite 3-4 students to share their response for one of the pets, including how they determined the amount would be a reasonable estimate.