# Day 45: Flat Mirror Warmup & Spherical Mirror Play

Thursday, 17 October 2013

The big news today is the assembly we had that was devoted to robotics. Our goal was to gain student fans and I’d say our captains nailed it. Watch the recording here.

I had to teach a little physics today, too.

I love the way this section is working out this year. We learned ray tracing in a spherical mirror and the mirror equation on the same day. I had the kids work out the equation for the image of the smiley face above [get the Word version]. They computed an image distance then used ray tracing to check their answer.

Everything goes great until this one:

“Ms. H-G, why is the image distance negative?”

When I tell them the other images were real and this one is virtual, they want to know what the difference is. I tell them real images can be projected onto a sheet of paper and virtual ones can’t. They demand proof, so I grab the concave mirror, a model, and several students with flashlights. We held a sheet of paper where the real image formed and saw our model’s face on the page. Of course, this kind of thing doesn’t photograph well, so here’s an example I found online.

What was the warmup in 4th period?

We also watched a clip fromÂ Minds of Our Own (thanks, Frank!) starting around 6:30 about how backing away from a mirror doesn’t allow you to see more of yourself.