The purpose of this activity is to build students’ intuition for 1 gram, 1 kilogram, and the relationship between them. Students learn that 1 kilogram is 1,000 times as heavy as 1 gram. Students convert quantities from kilograms to grams, and compare quantities given in different units. 

A note about weight and mass:

In earlier grades, students learned that “weight” describes how heavy an object is and can be measured in grams and kilograms. Because this understanding is consistent with everyday usage and because students may not have learned the distinction between mass and weight, these materials continue to use grams and kilograms as units of weight. For students who can distinguish mass and weight, consider clarifying that weight can be expressed in grams or kilograms, assuming that it is measured at sea level on Earth.

If students wonder about the meaning of “mass,” consider explaining that it measures how much matter is in an object and is usually measured in grams or kilograms. Clarify that these concepts will be studied in a future science course.

As in earlier lessons, when an amount given in kilograms is a fraction ( or ), students are not expected to find its equivalent in grams by multiplying the fraction by 1,000. Instead they are to reason about the conversion, based on what they know about fractions and the number 1,000.

If possible, prepare one box or more of 100 paper clips or 250 paper clips, and allow students to feel and compare the weights of 1 paper clip, 100 paper clips, 500 paper clips, and so on.

MLR2 Collect and Display. Circulate to listen for and collect the language students use as they work to solve comparison problems, using “kilograms” and “grams.” On a visible display, record words and phrases such as “kilogramo", “gramo“, “veces“ y “unidad“ // “kilogram,” “gram,” “times as much,” and “unit.” Invite students to borrow language from the display as needed, and update it throughout the lesson.
Advances: Conversing, Reading

• “¿Cuál unidad es más pesada: un kilogramo o un gramo?” // “Which unit is heavier, a kilogram or a gram?” (kilogram)
• “¿Creen que su mochila es más liviana o más pesada que 1 kilogramo?” // “Do you think your book bag is lighter than or heavier than 1 kilogram?” (Heavier, because I have a lot of books in it. Lighter, because it’s empty.)
• Display the table and invite students to share their responses and their reasoning.
• Discuss students’ responses to the comparison problems.

Previously, students learned about kilograms, grams, and the relationship between the two units. In this activity, they develop their sense of 1 milliliter, 1 liter, and the relationship between them. They do so by observing the number of times a smaller container—with 1 milliliter, 20 milliliters, or 100 milliliters of liquid—needs to be filled to make a greater amount, up to 1 liter. Students see that 1 liter is 1,000 times as much as 1 milliliter, and convert quantities from liters to milliliters. When they visualize the relationship between liters and milliliters and use their understanding of this relationship to make conversions, students reason abstractly and quantitatively (MP2).

Videos that show liquid being poured are provided, but a live demonstration—if possible—is preferred.

• Select students to share their responses to the second and third sets of problems. 
• If no students use equations to show their reasoning for the second set of problems, consider writing them: , , and .
• Display and complete the table as students discuss their responses and their reasoning for the last problem.