Friday, March 09, 2012

Shadows on Planet Earth....

We just finished our unit on similar triangles, and as par for the course, there were the typical shadow problems. I know from past experience that students have problems with these: they draw shadows going in 2 different directions .... they don't know how to set things up .... etc. BUT. I thought it was a geometry misconception problem. No. From deeper questioning of various students today, I see that some students have no concept of shadows.

Various questions/answers:
* What makes a shadow ... or how is it made?
- shrug.

* How would you make your shadow longer if it's coming from a light post?
- move closer to the light?

* Draw the picture and point to the shadow.
- points to the hypotenuse.

How did I miss this scary fact in 12 years of teaching geometry? I guess I just made assumptions on why they were struggling, and didn't probe deeper.


  1. You can't be faulted for not having that tingling "spidey" sense of things being not in place; afterall teachers are humans. Peace.

  2. Wow. Just wow. I wonder if my students understand shadows.

  3. Charlotte Ealick1:09 PM

    That might explain a lot! My students might be having the same issues, and I never knew. Thanks for sharing! I guess all the shadow games we played when I was little had a greater purpose.

  4. Wow. I am forever amazed at misconceptions in math and science, though I know I shouldn't be.

    I'm with Charlotte: I immediately thought of shadow games as a child, and thought "If only these kids had played such playground games, they might have got shadows better".

    Thanks for sharing this - we all fail to recognize students' thinking until we delve deeper.