Lesson: Stopping the Sahara

Show students a picture of a famous basketball player, such as Dikembe Mutombo. Ask students to guess his height and weight. Then ask: If I told you that he weighs 118 and he’s only 2.18 tall, would you agree or disagree with me? Pause to see if students recognize that the figures do not include the units. Then explain it is true that Dikembe Mutombo’s height and weight measurements are 2.18 meters and 118 kilograms, which are equivalent to 7 feet 2 inches and 260 pounds. Tell students that it is important for them to pay attention to the units used because there are different units of measure used in different situations.

Tell students that they are about to watch a video in which a problem is being solved. Tell them to watch for a) the problem described in the video, b) the solution, and c) the other benefits this solution results in. Then play the video. Have an open-ended discussion afterward about the problem, the solution, and what they found interesting.

Have students read the article individually. Then ask the following discussion questions:

• What is the main problem discussed in this article?

• Why is the growth of the Sahara desert such a problem?

• What is the Great Green Wall?

• How has the project already shown promise?

Partner students up and tell them they will be tasked with writing steps for how to convert between metric and customary units while watching the video. Then play the video. Have students work with their partners to write the steps. Then have them compare their steps to the example box on page 15. Select a few volunteers to share how their steps were the same as and/or different from the example.

Read through the introduction and the example of the “Metric Conversions” box on page 15. Ask the following questions after each step:

• For Step 1, ask: Why do we need two conversions? (The conversion table doesn’t show a unit rate for a meters-to-miles conversion. So we need to convert from meters to kilometers and then from kilometers to miles.)

• For Steps 2 and 3, ask: Why are these units placed in the numerator and denominator? (So the meters unit cancels out and only the kilometers unit is left; So the kilometers unit cancels out and only the miles unit is left.)

Then have students work on the “Your Turn” questions individually. Provide students with calculators if you want them to focus on the conversion process and not the decimal multiplication and division.

Have students read the article “The New Kilogram” from our friends at Science World. Then have a class discussion about what they just read. In particular, discuss how metric units were determined and why scientists only use metric units. Then ask students why having commonly agreed upon values for measurements is important.

Provide students with a recipe that includes measurements with cups and teaspoons. Tell them that you only have tablespoons and fractions of tablespoons for measurement materials at homes. Provide them with the conversions 3 tsp = 1 tbs and 16 tbs = 1 c. Then have students rewrite the recipe using only tablespoons.