Do very tiny things have weight?
1. Ask the question
Begin by asking students to name some of the very smallest things they can think of. Once you have a list, ask students how much they think these things weigh — or whether they have any weight at all.
Introduce the investigation question:
- What if you can't feel any weight in your hand?
- What if you can't measure any weight in the pan balance?
- What if the object is lighter than 1 gram? Is there still weight?
Ask students what they think about the weight of something tiny, such as an eraser rubbing. After erasing something, do they think the tiny pieces of rubber that are left on the paper have weight? You may want to modify the posted investigation question to read, “Do eraser rubbings and other very tiny things have weight?
Detours: Some students may object to using the new weight lines. They may think that the new scale will somehow misrepresent the weights. Explain that unlike a meter stick or ruler, a weight line is not used to make measurements; it is used to display them. The spaces between gram markers can be any size as long as they are all the same size.
Have students exchange their ideas, but leave the questions unanswered. Let them know they will work with some tiny objects today. Show students the desktop weight lines they will use.
- How is this weight line different from the one we used last time, when we displayed the weights of the cubes?
- The whole numbers are much farther apart, and the upper limit is 4 grams.
- Do you think we can use this weight line to display very tiny things? Why or why not?
Show students the 8–gram piece of plastic modeling clay. Demonstrate how they might roll the plastic modeling clay, cut it in half, and place one half on the weight line in its proper place. Drawing attention to the oversized weight line you have drawn on the board, ask students, “Where will that first piece go? If you cut the remaining piece in half, where will the next piece go?”
When you have a consensus, draw circles at 4 grams and 2 grams on the class weight line. Before the class breaks into small groups, have students predict how many times they will be able to cut the plastic modeling clay in half.
- Will you run out of plastic modeling clay? Will you run out of weight?