Wednesday, November 26, 2014

Mirrors and Reflection; Make a periscope; Make a one-way mirror

There is so much to learn about mirrors and reflection! We really liked making this periscope for an activity. (You can find instructions for a similar periscope here.) We wished it could have been even longer, but longer periscopes make the image you see even smaller, so maybe it wouldn't have been as cool as we thought.
More resources on reflection: 

Video about How mirrors are made

Another (sort of silly) video on how mirrors work

(As I mention on the telescope post, the videos here on how liquid mercury mirrors are made are very interesting also.)

This page talks about different types of reflection (specular vs diffuse)

This page is great—lots of good diagrams, explanation of what is happening in convex vs. concave mirrors, why mirrors reverse what we see, etc.

The children were always asking about how the auto-dimming rearview mirror in our car worked, and I had wondered a lot about it myself! We found a couple sites that explain it well: here and here.

We also talked about one-way (or is it two-way?) mirrors. The kind that look like a mirror on one side, but you can see through them like glass on the other side. :) 

This site gives a good explanation of how they work, as does this one. The basic idea is that you need a very, very thin film of reflective material—so thin that with a strong light on one side, you can see through it, but without that back light, it reflects light like a mirror would.
Knowing this, you can make your own fairly easily. We got it to work, though not perfectly. We took a clear piece of glass from a picture frame and covered it with thin Mylar sheets (something like this) on one side. It worked just like a mirror when the lighting on both sides of it was consistent. Thus you can see me in the mirror, taking a picture with the camera. (left side, above)

However, when we dimmed the lights on one side, and turned on a bright lamp on the other side, the "mirror" became more of a "window," and I could see Abraham looking at me through it (right side, above).

Tuesday, November 25, 2014

Polarization of light

Polarization is one of those things I assumed I understood but I really didn't. Sam is always going on and on about it (every time he wears his sunglasses he notices some new effect to make observations about) but now I finally, at least somewhat, understand what is making these effects occur! 

We watched this Happy Scientist video, and then this one, which gave great explanations of what is happening when light is polarized. He describes the phenomenon of birefringence (which is what we're seeing in that CD case pictured above—the photograph was taken through our polarizing filter) and shows how you can use two polarizing films together to twist the light back so you can see through it again! Like this:
Polarized sunglasses: at this angle they are darkening the computer's LCD screen slightly, but not blocking all the light, because they aren't turned in the same direction the (already-polarized) light from the screen is coming from.
When we turn the glasses, they now block all the polarized light from the screen.
But, if I hold another polarizing film up behind the glasses and twist it at an angle halfway between the others, it actually undarkens (??) the screen, and makes a window we can see through! So cool!

A few more good links: 

A video about polarization filters

This experiment shows how you can change the direction of polarization in light

A website entirely about polarization

Monday, November 24, 2014

Interference effects and light

Any discussion of wave-particle duality has to include the famous two-slit experiment! This is one that's pretty easy to replicate at home (well, part of it, anyway) and it's cool to see the interference pattern demonstrating the wave property of light!

There are several good ways to do this demonstration: this one here is clear and easy to follow.
You can also look at diffraction patterns using these instructions here.
Light viewed through a diffraction grating

For a clear visual demonstration of how interference effects make patterns, you can use these printable moiré patterns. I love moiré patterns—my dad had a whole book of them where you moved one film on top of another to create those strange moving shapes. They can be very beautiful and elaborate. The idea is really the same as the interference you get with waves of light: two superimposed peaks create darker patches, a peak and a trough superimposed cancel each other out. A good explanation is here

To make these moiré patterns, I just printed off several pdf files from this site onto transparency film (this kind worked great for my printer). When you move and rotate the different patterns on top of each other, you get various beautiful moiré effects.

Here's a short video of how the patterns change as you move them around. So pretty!

We also talked about thin-film interference, or iridescence. This page has a good explanation of why iridescence occurs in soap bubbles, peacock feathers, etc., and this article discusses the same effect.

Friday, November 21, 2014

Light and Shadows

There are lots of fun activities to teach kindergartners and preschoolers about shadows, but even though the concept seems simple, there is a surprising amount of information to learn for older kids too. For example, can "the speed of dark" actually move faster than the speed of light? That's the subject of this fascinating video…it will make you question all your assumptions for a minute or two. :) 

We had fun doing shadow puppets on the wall—we got some ideas here, but the children also loved making up their own, of course!
Our favorite thing was watching some videos of professional shadow puppeteers (?)—the shapes they can make are AMAZING! And they move between shapes so fluidly! It is really fun to watch:
Here, here, here, and here (this one is cool because you can watch the guy as he makes the shadow pictures with his hands).

We also experimented with what kinds of light make harsher and softer shadows. We used the camera flash and Sam's big reflector to compare direct and indirect light, diffused light, artificial light and sunlight, etc., and how those different lights affected the look of photographs. We tried bouncing the flash off of various surfaces to see how that changed things, too. The children always love being able to use the camera, so this was a big hit.
Abe in various kinds of light, taken by Malachi

Malachi in various kinds of light, taken by Abe

Wednesday, November 19, 2014

Sources of Light

Near the beginning of this unit we went through a general overview of different sources of light.

Besides the sun and fire, there's chemoluminescence, fluorescence, and bioluminescence. Glowsticks use chemoluminescence by mixing two reactive chemicals that release energy when combined. There is a good explanation here:

How glow sticks work

And a video on how you can make your own glowsticks, here. You have to have specialized chemicals and it's not super easy to make them, so it's not something we wanted to try, but the video is still interesting.
When we examined the glowsticks closely, we could see the small inner container which breaks when you bend the glowstick to activate it.

Here are some interesting videos about bioluminescence:

Animated video showing different animals that bioluminesce (good except that the narrator has a strange fixation with talking about "raves," for some reason)

This one is really short and you'll want to turn down the sound to avoid the swearing. But it's cool to see algae suddenly light up blue when the water is disturbed.

This video shows someone swimming among the bioluminescent dinoflagellates—gives a better idea of how huge some of these masses are

And, since none of us have ever seen fireflies in real life, we watched this video showing what they look like (there were some in Utah a couple years ago!)

This page has a good diagram showing one way atoms make light (fluorescence), along with a good overview of what light is.

And here's an explanation of how "black lights" work.

Tuesday, November 18, 2014

Light and Optics Unit Schedule and Lesson Plan

Light is so fascinating. And I'm so unqualified to teach it! My Dad was a physicist, my three brothers are physicists, my husband is an artist who specializes in teaching how to capture lighting effects in art, and ALL of them know so much more about light than I do that I really wished I could just turn this whole subject over to them to teach. But, as always, I just got hundreds of books from the library, read everything I could find, watched lots of videos, and hoped it would be enough. I also asked my "panel of experts" lots of questions as I went. :) I know that some of the concepts we learned in this unit are oversimplified and maybe even inaccurate because we are having to simplify them so much, but we've really loved this unit anyway, and I hope it will be a good foundation for MORE in-depth study later on.

For example, any unit on light has to include a discussion of wave-particle duality. After reading some books and talking about different behaviors of light that demonstrate each of those characteristics, we watched videos like this one, on "Schrödinger's Cat," and this one, on the Heisenberg Uncertainty Principle. They're a bit advanced for the children (and even for me, really) but they introduce fascinating concepts anyway. Although Malachi did say after Schrödinger's Cat, "I wish you'd never told us ANY of this!" :)

Probably our favorite video was this one about wave-particle duality. I think my brother would disapprove somewhat of all these videos because they focus more on the "weirdness" and flashiness of all these concepts and less on the principles behind them. And probably because again, in trying to simplify or popularize a concept, we are losing accuracy. (Which is the fundamental problem with all TED talks, come to think of it.) But I've always loved the idea of wave-particle duality (in all its weirdness) and I was pretty sure at least the older kids would be fascinated by it too, so…sorry, Karl. :) Karl maintains that the only way to truly understand physics is through mathematics, and without the right math, there's no way to fully make sense of it all. He says it gets much easier to understand once you have the math, too, since calculus is a language made up especially for the purpose of expressing concepts of physics. But since none of the children are old enough for calculus yet (and I've forgotten all my calculus, more's the pity), we have to bungle along without complete understanding, for now. It was very helpful to write to him in all my confusion about various concepts and have him say things like, "Just don't even worry about that yet," or, "For now, all you need to know is ____." There is just so much to learn!!

The Happy Scientist has some great resources on light (scroll down to see the list)—both videos and written experiments. I think you can access the written experiments without a subscription, but we love his videos too and find the subscription price well worth it.

This is a great chart for reviewing the entire electromagnetic spectrum.

If it had been summer, we would have liked to make a solar oven when talking about lenses and parabolic light collectors. From what I read, you have to have pretty hot temperatures (like above 85F) to make something like this pizza box oven work. So we'll hopefully get a chance to try it another time. Here's a video about focusing sunlight, as you would for a solar oven or a solar heater.

Here is some stuff you can get to help you learn about light and optics. We were happy with all these things, as they allowed plenty of exploration and allowed us to do all kinds of projects and experiments:
  • First of all, we have this (relatively) high-powered laser pointer. You can do most projects with a cheaper, flimsier laser, but since we all like this sort of thing, we wanted the nicer one. Also, the laser projection microscope experiment is more impressive with a higher-powered laser. (And it's great for astronomy!)
  • We liked this light experiment kit, which comes with ideas for how to use the components to learn about light. It has a diffraction grating and polarizing film and some lenses (not great ones).
  • These color paddles are fun for learning about color mixing, etc.
  • These lenses and prisms were a lot nicer than the others. Great for seeing refraction. We liked how they show a "cross-section" view.
  • We also have a heavier glass prism like this (Sam uses it for his class).
  • This is a good, compact but bright flashlight we used for lots of things.
  • You can request a free video on optical engineering here. I just emailed and they sent it right to me. It looks like they have free posters available as well.

Friday, November 7, 2014

Reading Bearathon

On the last day of our unit, we had an all-day readathon—reading marathon—well, all right, we just went ahead and called it a "Bearathon." We made hot cocoa in the crock pot, the children made cozy little nests, and everyone just read and read and read. It was great.
Abe's slightly over-ambitious stack of reading material
Marigold, seeing all the bears around, decided it was a sort of Bear Buffet from which she could take her pick of bears. She was so happy!
So much fun!

Tuesday, November 4, 2014

Famous Bears

There are so many great bears in stories! We talked about some of the most famous ones like Winnie-the-Pooh and Paddington. 

We've always liked Smokey the Bear
More about Smokey
And some pretty awesome old advertisements for him here.

We enjoyed the movie A Bear Named Winnie---it's based on a true story about a Canadian Bear that ended up in the London Zoo. (And the real Christopher Robin, A.A. Milne's son, did indeed visit this bear and re-name his own bear, Edward Bear, after Winnie.)

We watched, and liked, Disney's "Bears".

We also really liked Bears of the Last Frontier—all three episodes.

Monday, November 3, 2014

Gummi Bear Graphing

There's a pizza buffet we go to sometimes which, for awhile (before they took the costs of my children into account, presumably) had Gummi Bears as one of the "salad bar" items. (??) The children treated them like manna from heaven. They'd get a bunch of gummi bears and then line them up in rainbow order and compare them with each others' and eat them carefully one color at a time.

So, I decided to buy a bag of Gummi Bears and put all that OCD behavior to good use making graphs. We created various types of graphs and charts of Bear Color, and made estimates, and drew conclusions, about the number of bears per color per bag. Very interesting (and the children thought the bears were SUCH a special treat!).

Saturday, November 1, 2014

Teddy Bear Picnic

Bear buns. Just a regular roll recipe, shaped like bears by sticking on balls of dough for the ears and muzzle (though there are a few definite NON-bears on this pan---a monkey and at least one pig).
On holidays we usually have some sort of school party, and Halloween fell during this unit, so we took the not-terribly-creative course of having a Teddy Bear's Picnic. (It was the most beautiful of Indian Summer days! Positively hot outside!) I'm really not a very good or motivated "party planner," but I'm willing to go to a little extra effort if it seems like it will be worth it. And for a Teddy Bear Picnic, there is so much cute Bear-themed food you can find ideas for! Also, we already had lots of bear costumes around, so the children had no trouble disguising themselves. 
We got out our parachute and played games with it. The stuffed bears got bounced on top and had quite a fun time doing so.

We didn't eat all of these foods at our picnic (the bear buns and the pancakes were actually on other days), but all of them would have worked nicely for it.
We cut out bear-shaped toast with cookie cutters.
Bear pancakes (another day)—they were cuter here.
The best parts of the Teddy Bear Picnic, in Daisy's opinion, were the invitations. A big one for each child—a smaller one for that child's bear—and an even tinier one for that bear's bear. I just made them out of bear silhouettes.
I just used bear silhouettes and typed words on them (obviously).
We had this delicious pudding with berries on it. Again, the main attraction was that there were tiiiiiny sizes—so the children could feed their bears too.
The bears liked it. They liked their bowls of one Gummi Bear and one Teddy Graham, too.
A bear.
Hey, how did these monkeys get in?
It really was a great picnic (and Halloween Party)!

And furthermore, on the subject of Teddy Bears:

History of the teddy bear—we also had several good books from the library about Teddy Roosevelt and the story of the first Teddy Bear

Project Teddy Bear, sponsored by the Bank of American Fork. We're going to donate to this at Christmastime this year.
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