How do we measure objects of different sizes? How do we compare one measurement to another?
Do Now: (Have rulers, yardstick and tape measure hanging in front of the class) Make a list of the names of these measuring tools, and how long you think they are. Bonus: Write down the names of any units of measurement that you know.
Motivation: When would it be helpful to know how long something is?
Lesson/Modeling:
• Ask students: Do we have to use a ruler to measure? Let’s think about other ways that we can measure things.
• Ask students for other ideas for units of measurement, i.e. “thumb,” “hand,” “pencil,” and record student’s suggestions on a large piece of paper or chalkboard.
• Model using your finger to measure the length of a book (It’s two and a half fingers long).
• Have students use an informal unit to measure the longest edge of their desktop or table. Each student or group of students should use the same informal unit, for example each student should use a hand, or a finger, or a pencil as their unit, but they should each use their own finger or hand so that the resulting measurements vary. Have students record their measurement. Move among students to observe and assist if necessary.
• Have students use a ruler to measure the same edge to the nearest inch. Record the measurements.
• Bring the class back to order and compare the resulting informal unit measurements with the standard unit measurements. Ask students what they notice about the results. Ask students why they think we might use standardized unit labels for measurement. What are the pros and cons? Can you think of some situations where it would be okay, or better, to use informal units for measurement?
• Using an everyday object (a book, desktop, computer monitor, chalk board) ask students to estimate the lengths or measurements of the object. Records the estimates on a large sheet of paper or the chalk board.
• Ask the students to relate their estimates to the measuring tools or to the other objects when making a guess. How many squares long is this textbook? How many rulers would it take to reach the end of the chalkboard?
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