My friend and fellow physics teacher, Dan Burns of Los Gatos High School, mentioned using a large Fresnel lens to burn gum off the pavement outside his room.A few years ago, my school purchased new overhead projectors for the classrooms. I shuddered at the thought of all the old OHPs going to the landfill. I intercepted as many as I could and salvaged the optics from them.
The harvest was bountiful. It included the Fresnel lenses that formed the stages of the OHPs.
Hence the community service project outside my classroom last week.
Two lessons to take away? One: always be on your toes for potential harvests of otherwise unwanted or unused school equipment. (I similarly collected dozens of headphones when the school purchased classroom PCs.) Two: it's nice to have bright folks like Dan Burns to get clever ideas from.
Funny. My students were outside on Friday with salvaged Fresnel lenses from discarded overheads. I had to gain access to the temporary storage shed to scavenge the lenses, but what a bounty!
ReplyDeleteWe were merely determining the focal length of the lenses using some good, old-fashioned paper. But my students noticed some interesting things: 1) lined, 3-hole paper didn't ignite as well as copier paper. We never did figure out why. 2) If you put a black mark on the paper with a Sharpie, it ignited immediately. A great inquiry discovery by some smart physics students.
Hey Chris, good physics!
ReplyDeleteTechnically, my students *were* determining the focal length of the OHP Fresnels. They just weren't measuring the exact numerical values.
I can almost smell the burning gum. Please cut me in when you market this device.
ReplyDeleteHey Dan,
ReplyDeleteYeah--the kids were pretty well cured of their gum-chewing needs after that! I had to hose 'em down with Febreze before letting them back in my room.