Bat Signals

I'm doing a craft project for Batman's 75th Anniversary where the kids are going to make Bat Signals out of Pringles cans. I had two different kinds of Pringles cans: a short one and a long one. I wanted to see, which can produced a clearer bat signal when an LED keychain flashlight was placed inside?

Well, the first thing I had to do was construct a "stand" for the flashlight so that it would shine directly upwards. It kept falling down, ruining the effect! I cut out two circles (using the Pringles lid as a guide) of cardstock, glued them together so that they would be sturdy, and folded them into a semicircle shape. With the fold I cut some slits going outward in a kind of star formation so that the flashlight could poke through. Then I taped all around and underneath. Finally, I cut a few more slits around the outer circumference of my circle and bent the sides down like a hexagon to make it into a "stand." Worked quite well and I don't forsee having too difficult a time helping the kids to do this.

Next I experimented with my different sized Pringles cans. The long one worked just fine, but I wondered how the small one might work? As you can see, not well at all!

I was really puzzling about this because it seems counterintuitive that the longer tube would produce a clearer image (given how light tends to dim and spread when it comes from a longer distance). Then I did some Internet searching and sure enough, if your goal is to generate a clear, undistorted shadow, you actually want your light source to be farther away. That is why the sun makes very accurate-sized shadows of birds and things hovering overhead while a light bulb would not--because the sun is millions of miles away.

This comb example from helped clear this up for me considerably. My light source (in the short can) was TOO CLOSE to the bat symbol and ended up distorting the shadows. To get a clear and exact shadow, you want your light source to be far away but channeled (a task for which a Pringles can proves very handy!).

This could even be observed when I raised the height of the flashlight in the long can. Using glue sticks I created a higher stand for my flashlight, dropped it in, and sure enough the image was a bit more distorted and blurry from the light waves hitting the batman picture and sending shadows in all directions:

So in conclusion, the kids will definitely be using the long Pringles cans on Wednesday!


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