Which Picks Up More?

Est. Class Sessions: 4–5

Developing the Lesson

Part 1. Introducing the Lab

Discuss the Better “Picker Upper.” Students will investigate the absorbency of three brands of paper towels by measuring the area of the spots formed by drops of water. They will investigate further by seeing how many of these spots fit onto a paper model of a towel.

To begin the discussion, read the opening vignette and Question 1 on the Which Picks Up More? pages of the Student Guide. Professor Peabody decides to investigate different brands of paper towels after he cleans up a spill in his lab with one that is not very absorbent. Students will conduct an experiment similar to Professor Peabody's. The discussion of Question 1 should lead students to conclude that they and Professor Peabody are interested in finding out which paper towel can pick up or absorb the most water.

Include in your discussion other questions such as:

What do you think Professor Peabody's paper towels looked like after he used them to clean up the spill? (soaked with water; no dry area left)
Why is he interested in finding the better “picker upper”? (Possible response: He wants a paper towel that can pick up a lot of water. He doesn't want to use a lot of paper towels to clean up spills.)
How will you decide which paper towel picks up the most water? (The paper towel that can pick up the most drops.)
Is there anything that you can measure? (area, length, or width)

Ask students to do some preliminary observations by answering Questions 2–4. Distribute the extra sheets of paper towels and the small container of water and eye dropper to each group. To answer Question 2 students touch and look carefully at each brand. The sheets may differ in size, thickness, and puffiness. To answer Questions 3–4 students may make some additional comparisons by comparing the spots made by dropping water on each sheet. Discuss Questions 3–4 to decide how to measure the differences students observed in the spots.

Ask:

Are the spots the same size? Explain. (No, the spots vary in size from sheet to sheet.)
If the same amount of water is dropped on each sheet, why aren't the spots the same size? (The water spots spread out differently on each of the paper towel brands. Some spots spread to cover a large area, and some do not.)
How can you measure the size of the spots (Question 4B)? (Measure the length, width, or area of each spot.)
What are the advantages and disadvantages of measuring the length or width of each spot? (Length is one easy measure but each spot may not be the same length in each direction. It also may be difficult to find the longest length consistently for each spot.)
What are the advantages and disadvantages of measuring the area of each spot? (Area can describe the shape well, whether or not the shape is “circular.” Area is easy to count. Area also relates to the question we are trying to answer: which picks up more.)
How can we measure the area of the spots? (Have students share their ideas. Students may suggest cutting out the spots, tracing them on Centimeter Grid Paper, and counting square centimeters.)
Will knowing the area of the spots on the different paper towels help determine which brand picks up the most water? (Possible response: Yes, because if helps me figure out how many drops of water might fit on each brand of towel.)

Use The Better “Picker Upper” Lab with Feedback Box in the Student Activity Book to assess students' progress toward the following Expectations:

Find the area of a shape with curved sides [E3].
Make a scaled bar graph [E5].
Read a graph to find information [E6].
Find the median of a data set [E7].
Make predictions and generalizations about a data set using tables, graphs, and diagrams [E8].

Prepare to Draw the Picture. Ask students to remove The Better “Picker Upper” Lab pages from the Student Activity Book. Ask students to discuss Questions 1–2 with their group before they start to draw a picture for this lab. To answer Question 2 about fixed variables, students may need to work with the materials to make spots. After groups have had a chance to brainstorm some ideas, make a list of student responses. Be sure they include the following:

Use water on all the paper towels. (A liquid with different properties might spread out differently.)
Use 5 drops to make each spot. (More water might make larger spots. Then we cannot compare the areas of the spots.)
Drop all the drops in the center of each spot. (We want to see how far the water spreads out from where the water is dropped. We want the water to make its own shape.)
Use the same type of eyedropper. (This keeps the size of the drops the same.)
Keep the towels off the desk until the spot has stopped spreading. (This will ensure that the water will spread out on the paper towel and not on the desk. See Figure 1.)

Draw the Picture. Ask students to draw the variables and tools they have already identified. After you demonstrate the lab procedures, students will add to and refine their drawings. See Figure 2 for an example of a finished drawing. Students should be able to show the types of paper towel, the tools, and the fixed variables.

After discussing the variables, model the procedure students will follow for collecting the data. Each group will have one sheet of each of the different brands of paper towels. Label the three brands of paper towels clearly. Because more than one water spot will be made on each paper towel sheet, sheets should be kept off the tabletop so that the spots do not run together. To facilitate this process, students can place two books on the table, spaced a little closer than the width of one paper towel. One edge of a sheet is placed between the pages of each book so that it is lifted off the tabletop, as in Figure 1.

If students write the brand name on each sheet of paper towel as they receive it, they will have fewer problems remembering brands later. It is also a good idea for student groups to write their initials on the paper towels.

Another method is to lay the paper towels on top of geoboards. Demonstrate the following process to students:

Label the paper towel with the brand and student group name.
Use the eyedropper to drop 5 drops of water onto the paper towel.
Drop all drops in the center of each spot.
Wait until the spot spreads out.
Move to another section of the paper towel sheet (far enough from the first spot so that they will not run together) and drop 5 more drops.
Make three spots on each brand of paper towel.

As soon as the spots stop spreading, show students how to trace the perimeter of each spot with a pencil. This provides an outline of the spot's perimeter that will be visible once the water evaporates. Letting the paper towels dry for several minutes or overnight will make it easier to cut out the spots.

Using the spots you already prepared or when the spots are dry enough, show students how to cut them out and trace them on to a piece of Centimeter Grid Paper. See Figure 3. Also show students how to label their spots and paper towels with their initials and the brand of the paper towel. Ask students to add these additional steps and tools to their drawings.

In the sample picture in Figure 2, Daniel has shown the procedure and labeled the three brands of paper towels clearly. By looking at the picture, we know that he will drop 5 drops of water onto a paper towel, three times to make three different spots. He will use scissors to cut out the resulting spots. He will place the spots on grid paper to find the area in square centimeters. Daniel clearly labeled the two primary variables: “T = Brand of Towel” and “Area in sq cm.”

Divide and Conquer. Ask student groups to distribute tasks to collect all this data in a reasonable amount of time. For example, ask one student to help get paper towels ready (labels, suspending), ask another student to be responsible for the dropper and watching the spot spread and another student to outline the spot with a pencil and set aside for drying. Students can then divide up the task of cutting out, tracing, labeling, and counting the areas of each of the nine spots.

Student Guide: 102 103

Answers