Unit 2, Lesson 19
The Shadow Knows
Accelerated 7
Preparation
Lesson Narrative
The purpose of this lesson is for students to interpret real-world data and use what they’ve learned about similar triangles to justify why a given relationship is proportional.
In this lesson, students examine the lengths of shadows of different objects. There appears to be a proportional relationship between the height of an object and the length of its shadow. Students must justify the proportionality of the relationship by interpreting real-world data and making simplifying assumptions (MP4).
Students then use this relationship to predict the height of a lamppost given the length of its shadow. Finally, in an optional activity students go outside and take their own measurements of different objects and the lengths of their shadows and use this technique to estimate the height of a tall object (MP4).
This lesson is optional. Use this lesson anytime after Lesson 17.
- Calculate the unknown heights of objects by using proportional reasoning and explain (orally) the solution method.
- Justify (orally) why the relationship between the height of objects and the length of their shadows cast by the sun is approximately proportional.
Let’s use shadows to find the height of an object.
Required Materials
Activity 3
Activity 4
Required Preparation
Before doing the last activity, conduct the experiment ahead of time to ensure that shadow lengths will be cooperative at the time your class takes place. Also, make preparations to take your class outside. They will need measuring devices (tape measures, yard sticks, rulers) as well as a way to record their measurements. Provide access to tape measures, yardsticks, or rulers.
Before doing the last activity, conduct the experiment ahead of time to ensure that shadow lengths will be cooperative at the time your class takes place. Also, make preparations to take your class outside. They will need measuring devices (tape measures, yard sticks, rulers) as well as a way to record their measurements.