Grams and Kilograms - math grade 2 - lesson 51

In today’s lesson, students are introduced to measuring the mass of objects using various benchmark items that are 1 gram or 1 kilogram. Students build understanding of grams and kilograms and use what they have learned to decide which unit is appropriate to use when measuring items. Gram and kilogram units are often referred to as “weights,” but they are actually measures of mass, or how much matter is in an object. An object’s MASS is consistent and unchanging no matter where the object is—on Earth, on a mountain, at the bottom of the ocean, or on the moon. However, an object’s WEIGHT can change. For example, an object has a different weight on the moon than it does on Earth due to the effects of gravity. 

Note to the Teacher: Since students are measuring all objects here on Earth, it is okay if they use the word weight from time to time to help them build understanding of mass. However, remind them that mass and weight are not the same.

1.TEACHER SAY: We have spent several days learning to measure the length of items. Whisper to your Shoulder Partner the two units we have used to measure length.

STUDENTS DO: Whisper to their Shoulder Partner the two units they have used to measure length.

TEACHER SAY: Good. We use the centimeter to measure shorter items and the meter to measure longer items. Today we will be learning to measure the mass of items. Say “mass” with me.

STUDENTS DO: Say: mass.

TEACHER SAY: Some people think mass is the same as weight, but it is not. Mass is the amount of matter—or stuff—something has. We can say that an object has mass that makes it show a weight of 10 kg. But mass and weight are different. Mass stays the same no matter where you are. If you are on Earth or the moon, your mass does not change. However, if you are on the moon, your weight will be different because the pull of gravity is different. How many of you take baths or have gone swimming before?

STUDENTS DO: Raise hand if they take baths or have gone swimming.

TEACHER SAY: Have you noticed how your body seems lighter in the bathtub, pool, or ocean? Even though your weight feels lighter, your body has not changed. Your mass—the amount of stuff in you—stays the same. We may use the term weight when we talk about mass because it helps us think about mass and because we are going to stay right here on Earth. However, it is important that you understand that weight and mass are not the same.

TEACHER DO: Display real-world examples or standard units of gram and kilogram.

TEACHER SAY: When we measure mass, we use grams and kilograms. One gram is much lighter than one kilogram. In fact, it takes 1,000 grams to equal one kilogram. Turn and Talk to your Shoulder Partner. Tell them something you may have seen or heard being measured in grams or kilograms. Give me a Thumbs Up when you are ready.

STUDENTS DO: Turn and Talk to their Shoulder Partner about items they have seen or heard being measured in grams or kilograms. Give a Thumbs Up when ready. Selected students share their thoughts.

TEACHER SAY: Thank you for sharing your ideas. You are going to work in groups today, so let’s get into groups now.

TEACHER DO: Use Calling Sticks or have students Count Off to form small groups of 4 or 5 students. Hand out benchmark weights (real-world items) of 1 gram to each group.

STUDENTS DO: Move to work with their small group.

Note to the Teacher: If you have standard units for grams and kilograms, hand these out as well to allow students to compare the mass of the standard units to the benchmark weights. If necessary, substitute the items referenced in the lesson as benchmark units with items that are more familiar to students.

TEACHER SAY: We use the gram to measure objects with less mass, which are lighter objects. One gram weighs about the same as one paper clip, one pen cap, one raisin, or one thumbtack. Each of you hold the item I gave you so you can feel its mass.

TEACHER DO: If you gave students more than one item, encourage them to compare them by holding one item in each hand.

STUDENTS DO: Explore the benchmark, real-world weights of 1 gram with group.

TEACHER SAY: Grams are often used when we use a recipe to cook. The recipe may call for 3 gm of sugar. We use the letter g to stand for grams. What are some other items you can see from your desk that you could measure using grams? Look around and think for a moment, and give me a Thumbs Up when you are ready.

STUDENTS DO: Identify items in their classroom that they could measure using grams. Give a Thumbs Up when ready. Selected students share their thinking.

TEACHER DO: Hand out benchmark weights (real-world items) of 1 kilogram to each group of students.

TEACHER SAY: We use the kilogram to measure heavier objects. One kilogram weighs about the same as one pineapple, a baseball bat, a 1-liter bottle of soda or water, a bag of rice, or a textbook. Let’s hand these items around the table so you can each feel their mass.

TEACHER DO: If you gave students more than one item, encourage them to compare them by holding one item in each hand.

STUDENTS DO: Explore the benchmark, real-world weights of 1 kilogram with their group.

TEACHER SAY: We use the letters kg to stand for kilograms. What are some items you can see from your desk that you could measure using kilograms? Give me a Thumbs Up when you are ready.

STUDENTS DO: Identify items in their classroom that they could measure using kilograms. Give a Thumbs Up when ready. Selected students share their thinking.

TEACHER DO: Select one of the gram items and one of the kilogram items students identified. If they were not able to identify any items, use two of the benchmark items. Either draw the items or write their names on the board with a blank space in the middle as shown below.

TEACHER SAY: We are going to compare the mass of these two items and use our greater than and less than symbols to express the comparison. When an item has less mass, we can say it weighs less. When an item has greater mass, we can say it weighs more. If I am comparing the_____ (gram item) and the _____ (kilogram item), which item has greater mass? Raise your hand if you think you know and can explain why you think so.

STUDENTS DO: Raise hand to volunteer. Selected students share their answers and explain their thinking.

TEACHER SAY: Yes. Which symbol would we use to make our statement on the board correct?

TEACHER DO: Use Calling Sticks to select a student.

STUDENTS DO: Selected student answers the question.

TEACHER DO: Draw the correct symbol (< or >) in the blank.

TEACHER SAY: Let’s explore these units of measurement more. Take out your student book and turn to page Lesson 51: Apply.

STUDENTS DO: Take out student book and turn to page Lesson 51: Apply.

TEACHER SAY: You will see pictures of eight different items. For each item, decide if it would be better to use grams (gm) or kilograms (kg) to measure its mass. Imagine that the items pictured are real, not toys or images.

STUDENTS DO: Decide if grams or kilograms should be used to measure the mass of each item. Circle their answers.

TEACHER DO: Walk around the room and offer help as needed.

TEACHER SAY: When you are finished, compare your answers with your Shoulder Partner.

STUDENTS DO: Compare answers with their Shoulder Partner.

TEACHER DO: If time allows, go over the correct answers with the class.