Hand a gram weight to each child.

• Is there is anything else you can think of that might weigh about the same as this piece of plastic?
• How does it feel?

Tell students they are now holding a piece of plastic that weighs 1 gram. Scientists and many people in the world use grams to describe the weight of objects. Distribute large paper clips (1.2 grams) to the students to provide another example of an object that weighs about a gram. Mention that most things in the classroom weigh more than one gram, and that students will have a chance to weigh some of them later today. Students will now use grams, not steel washers, paper clips, or bears, to describe how much something weighs.

• Why do you think it might be better to use grams instead of paper clips, washers, or plastic bears?
  (scientists and most people in the world use grams to weigh things)
• Are you more used to hearing about “pounds” when someone is talking about measuring weight?

Explain that a pound is a different unit of weight, much heavier than one gram. One pound weighs 454 grams. A gram is a fairly small unit of measure that will help them compare weights even when the difference is pretty small.

Show students the rest of the weights in the gram weight set: the 5–gram, 10–gram, and 20–gram pieces. Hand around enough weights for each student to experience the different weights. Think together about classroom objects that might weigh 5 grams, 10 grams, or 20 grams? Use a pan balance to check the guesses.

Introduce the investigation question: