Recall the last two investigations. In the first one, students weighed four samples of earth materials and entered the data in a class table. In the second one, they thought of some good rules for weight lines.

Today, they will make their own weight lines and use them to plot their data. Ask students to imagine how the project will go. If they need help, refer them to the class list of rules from the previous investigation.

• Where will you find the weight data?
• What will you do first? Then what?
• What do you think will be the hardest part?
• What do you think you might learn?

Introduce the investigation question:

What can a good weight line show us about our earth materials?