The title is a little misleading because today’s class had nothing to do with the Real Science Odyssey Physics curriculum. This was the last class of the summer and since most of the kids in the class already seemed to know a lot of the science we had been discussing I decided to do my light lecture for older kids. We discussed how light is a wave and why objects appear to be a certain color. For example, a blue ball looks blue because it reflects blue light and absorbs the other colors. I then asked why is the sky blue? Quite a few of them knew it had something to do with the atmosphere, but couldn’t really explain it, so I showed them my big tank of science… an aquarium filled half way with water and a bit of powdered milk mixed in. The powdered milk helps scatter the light. You can see in the first photo the milky water looks very blue near the flash light because the particles floating in the water are predominately scattering blue light. But if you look at the flashlight from the far end of the tank it looks orange/yellow… kind of like a sunset. When the sun sets the light reaching our eyes has gone through a lot of atmosphere (or a lot of milky water) before we see it and all the blue light has been scattered away, leaving behind the yellow/red colors. This is also why sunsets are more spectacular when there is a wildfire or volcano because there are more particles in the air scattering light.
After explaining polarized light with the help of some pvc (check out this link and photo below from Scientific Exploration with Paul Doherty) I gave each student a set of polarizers and showed them how when they are crossed they can block out all the sunlight. Then we put plastic forks between the crossed polarizers and you could see ‘rainbows’ of a sort in the plastic where it was stressed. This happens because the plastic is optically active, the light is actually rotated a bit as it passes through the plastic so it can now pass through the second polarizer.
We also talked about how rainbows are formed, how our eyes work and what it means to be color blind. There’s a great app on the iPad, ColorDeBlind, that lets you see how the world would look if you were colorblind. It doesn’t mean you just see black and white, it means that one set of color sensing cones isn’t as sensitive as its supposed to be. For some that means they have trouble seeing red, so a light pink shirt may look the same as a white shirt to them. Below is a picture I took with the app. The image on the left is what people with ‘normal’ vision see, and the image on the right is what a red-green color blind person might see. Notice all the reds and greens are gone but the blue stickers on the fruit still appear very blue. This really blew the kids away.
Physics Girl has a nice video explaining the physics of rainbows.
And the Royal Institute has a video called Light Fantastic: The Science of Color that covers a lot of these same topics.
This concludes this set of physics posts. I did not use the whole Real Science Odyssesy Physics curriculum since I was just teaching a short summer class. The kids I had in this class were already pretty versed in science, especially for only being 8 or 9 years old and they probably could have done with a little more meat in the curriculum. But if your kid has never done a science class this curriculum would be pretty easy to implement at home.