The Difference Between Mass and Customary Weight

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SWBAT use their shared understanding of mass to estimate the mass of given objects.

Big Idea

Mass and weight are different but it isn't obvious, so students need time to explore this idea.


10 minutes

What is estimation? Why do we estimate? Here we talk about approximate values, units and getting ‘close’ to the correct weight or amount.

How many counters do you think I have in this cup? Now how much water do you think is in this cup? What about how much this glass apple weighs?

We discuss how things can fill up a certain amount of space (liquid volumes) like pouring water into a cup, or how an object can have mass, which is different than weight. 

Building our Vocabulary

20 minutes

We create shared notes and definitions about the different between weight and mass because this can be a difficult idea for 8 and 9 year olds to grasp. I think it is important to take the time to do this so that we all have a shared resource that we can refer back to. 

Group Work

15 minutes

Please number your paper 1-5. We are going to use what we know about estimating today, and you’re going to have to use some really good thinking skills with your group today to figure these out! Remember to discuss together and defend your answers and ideas with our accountable talk sentence stems (Mp3)

1. What is the mass of a penny?

2. What is the mass of a pencil?

3. What is the mass of a school bus?

4. What is the mass of a rhino?

5. What is the mass of Mrs. Maffei?


5 minutes

What did you guys discover today? What made this activity challenging? How is mass different from customary weight? 

We spend some time at the end discussing the challenges of deciding between weight and mass and discuss why we refer back to our notes and new vocabulary to help us, especially with a new or difficult concept.