Lesson 19
The Shadow Knows
Let’s use shadows to find the heights of an object.
19.1: Notice and Wonder: Long Shadows and Short Shadows
What do you notice? What do you wonder?
![Photograph of 3 pens standing upright. Lamp on right. Longest shadow formed by pen on far left, shorter shadow on middle pen, no shadow on pen on right.](https://staging-cms-im.s3.amazonaws.com/dpKeHCHxeR5ThpW6zkoAJeDm?response-content-disposition=inline%3B%20filename%3D%228-8.2.D1.Image.01.png%22%3B%20filename%2A%3DUTF-8%27%278-8.2.D1.Image.01.png&response-content-type=image%2Fpng&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAXQCCIHWF37H2AMFB%2F20240727%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20240727T001747Z&X-Amz-Expires=604800&X-Amz-SignedHeaders=host&X-Amz-Signature=93c8026264895fddb76056753c32e35b4611221fa064fe4f13b6e8e3ad4811a1)
![Photograph of 3 pens standing upright forming shadows on the desk](https://staging-cms-im.s3.amazonaws.com/hucHV4yxHVBpo9Pjjxtk66tY?response-content-disposition=inline%3B%20filename%3D%228-8.2.D1.Image.02.png%22%3B%20filename%2A%3DUTF-8%27%278-8.2.D1.Image.02.png&response-content-type=image%2Fpng&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAXQCCIHWF37H2AMFB%2F20240727%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20240727T001747Z&X-Amz-Expires=604800&X-Amz-SignedHeaders=host&X-Amz-Signature=fe3c7c8838a817da4d7e38f8fe71185df99f2f3f2f6049f8aae87b9943d53b9e)
19.2: Objects and Shadows
![Photograph of 2 boys, a man, and a lamp post, each have a shadow to their left.](https://staging-cms-im.s3.amazonaws.com/jMFCcfQXzV7HHnohx2rdPfsE?response-content-disposition=inline%3B%20filename%3D%228-8.2.D1.Image.04.png%22%3B%20filename%2A%3DUTF-8%27%278-8.2.D1.Image.04.png&response-content-type=image%2Fpng&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAXQCCIHWF37H2AMFB%2F20240727%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20240727T001747Z&X-Amz-Expires=604800&X-Amz-SignedHeaders=host&X-Amz-Signature=cf1a68034591654b5ee15fc6807231d3587bec84b77e4b9ce4e4422f29e7246e)
Here are some measurements that were taken when the photo was taken. It was impossible to directly measure the height of the lamppost, so that cell is blank.
height (inches) | shadow length (inches) | |
---|---|---|
younger boy | 43 | 29 |
man | 72 | 48 |
older boy | 51 | 34 |
lamppost | 114 |
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What relationships do you notice between an object’s height and the length of its shadow?
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Make a conjecture about the height of the lamppost and explain your thinking.
19.3: Justifying the Relationship
Explain why the relationship between the height of these objects and the length of their shadows is approximately proportional.
![Photograph of 2 boys, a man, and a lamp post. Triangles drawn using person or post as height and its shadows as the base.](https://staging-cms-im.s3.amazonaws.com/mybn92VJ5qdLWyPvF1ZP6EwU?response-content-disposition=inline%3B%20filename%3D%228-8.2.D1.Image.05.1.png%22%3B%20filename%2A%3DUTF-8%27%278-8.2.D1.Image.05.1.png&response-content-type=image%2Fpng&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAXQCCIHWF37H2AMFB%2F20240727%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20240727T001747Z&X-Amz-Expires=604800&X-Amz-SignedHeaders=host&X-Amz-Signature=c8bcfe2c9fbed2ae0e6f949ff4c6b7b5d7a00ff6c8483cff4a85206f7f5f9142)
19.4: The Height of a Tall Object
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Head outside. Make sure that it is a sunny day and you take a measuring device (like a tape measure or meter stick) as well as a pencil and some paper.
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Choose an object whose height is too large to measure directly. Your teacher may assign you an object.
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Use what you have learned to figure out the height of the object! Explain or show your reasoning.