Friday, February 4, 2011

Not Enough Information?

My 9th-graders are great. Today was Day 2 of trig in H. Geometry (aka. the second day ever of SOH-CAH-TOA in their lives), and I nonchalantly left this as a Do Now on the board:

1. Do you have enough information to find the height of the flag pole?

2. Calculate the height of the pole. (Ask for more information if necessary.) Round to the nearest hundredths.

3. If this girl walks towards the flag pole until she has an angle of elevation of 50 degrees in order to see the top of the flag pole, how far away is she from the flag pole then?
By the time I finished checking off their homework from last night (3 minutes into class), they were already antsy for more information. I was glad! They asked me specifically for the height of the girl, so I gave them the height up to the girl's eyes as 145cm (note the intentional mix of different units... Kids are comfortable with conversions now after the Measurement Unit!), and they cranked away at the rest of the problem. After we went over the problem and everyone felt comfortable with all parts, I exclaimed that we were going to be building inclinometers today and that we would be going outside to do exactly this.* And kids were so excited!!

The inclinometers (aka. "sextants" in history classes) were a big hit. Kids liked them a bunch. Predictably, it took a while to build them in class, so we only had time to go outside to really measure one object in the last 15 minutes of class (...Our classes were also short today -- only 50 minutes on Fridays!), but I promised that we'll return to them next week to make more use of their inclinometers. (And we'll obviously also use them when we launch the cannons!)

By the way, my history teacher friends told me that these "sextants" (Is it just me, or does "sextant" sound like a naughty word?) have quite a bit of historical significance. The astronomers used them to help navigate the ships as efficiently as possible on their trade routes. Shorter trade routes = more profit for the company, so they were a pretty big deal back in the middle ages. Cool, eh? ...Obviously, I had to share that with my kids. Math + history = pretty darn cool. :)

*Here is an example of how a relevant Do Now avoided any need for me to explain procedures down the road. When we got outside, very few kids needed very minor reminders of what to measure! I also threw in there a phrase that they had never seen, "angle of elevation," and expected them to figure it out by context.


  1. Seem like a fun teacher! Found this looking up SoH cah toa which we are learning about now. Not the most exciting thing... (:

  2. Megan, SOH-CAH-TOA is one of my favorite topics in all of high school math!! I hope your mind changes about it soon enough. :)