Last week we used similar triangles to find the height of lamp post out front of the school:

**Act 1**

Scenario:

What do you notice about the lamppost? (FACTS) |
What do you wonder about the lamppost? (QUESTIONS) |

The pole is taller then the person | What is the height difference between to man and the lamppost |

It’s a lot taller then the person | how much taller is the lamppost compared to the person? |

its a tall lamppost | How tall is the lamppost? |

The iamppost tall than the boy | What height the lamppost and what the height of the boy |

there’s a person beside the lamp post | how much of that person does it takes to get the height of the lamp post |

The lamppost is tall | What is the height of the lamppost? |

What’s the height of the lampost | What’s the height of the lamppost |

– The post is taller than the person – The structure of the lamp post is sturdy |
– How much taller is the lamppost than the person?
– How tall is the lamppost? – How many persons will it take to reach the height of the lamppost? |

The lamppost is taller than the person | What is the hieght of the lamppost/person |

A person is next to the lamp | What’s the height of the person and lamppost? |

the lamppost is tall The lamppost is black |
How tall is the lamppost (who is that person) |

**Act 2**

Students were shown this diagram and asked which of these lengths/heights they could physically measure:

Then we headed outside to measure whatever we could with metre sticks & record on a handout of the above diagram in our small groups.

We returned to class & students solved at their boards (red/orange annotations on boards are mine during the whole class discussion afterwards):

We discussed the different boards & their strategies. We grouped the boards by strategy; proportion solving vs scale factor.

**Act 3**

The next day I poked a hole through a foam stress ball & fed some string through it – leaving the roll of string trailing behind. We went outside & took turns trying to throw the ball over the top of the lamppost. It took a good 20+ minutes, but we got it (“we” is a strong word since my throws did not work & my student Ahmed got it over!) and the students then measured the length of string that hung down to the ground; **10.16 m** was the actual height (which was fairly close to their solutions on the boards).

The rest of the day 2 class was dedicated to individual practice. Some students never completed the first practice from earlier in the semester on similar triangles, so they were assigned the basic exercise set on Khan Academy. Those that had completed that skill were assigned a more advanced exercise set involving similar triangles nested inside of one another.

Lesson materials available here.

– Laura Wheeler (Teacher @ Ridgemont High School, OCDSB; Ottawa, ON)