Weight Concept Cartoon

This cartoon was developed to assess students’ understanding of:

• the need for using standard units of weight
• the idea that the beam on a double pan balance is horizontal when the weights on each pan are equal

Student responses reveal whether they uncritically agree with all the characters, or have a more nuanced understanding of what makes a valid measurement. It is typically used after Investigating Weight 4, How much heavier is one cube than another?.

Things to look for in student responses

Sam:

Do students agree with Sam because the pan has “two cans”, or do they disagree, pointing out that the beam is not horizontal so they can’t weigh the same? Do they go even further and argue that the dog must weigh more than 2 cans because the dog side is down?

Carla:

Do students not only agree with Carla, but also give good supporting reasons — for example, noting that the beam is horizontal and the three cans are all the same size?

Napoleon:

Do students agree with Napoleon because the pan has “four cans”, or do they point out you can’t simply add the cans together because they are not the same size? Do they go even further and say that it looks like the dog weighs three cans, because the dog balances with two large cans plus two small cans (where the two small equal one large)?