We did more light investigations last week, starting with the good old "broken pencil" trick (see video below). As we know, as light travels through a medium (solid, liquid, gas), it travels in a straight line. When that light passes from one medium to another, the light changes speed. Light travels faster in air than in water. When light changes speed, it bends the light in a new direction. This bending of light is called refraction. The reason the pencil appears bigger and broken is because the light slows down as it moves from the air to the water. As light slows down or speeds up, the change in speed causes the light to bend. causing the pencil to look broken. Here is a cool video of a laser going from one medium to another, thus changing the speed and direction of the light. After the pencil experiment, the kids were given cups of water. See the video below to see how the scenario unfolded :) Initially the kids couldn't see the polymer beads in the water because the beads and the water bend almost at the exact same index of refraction. The light slows down as it enters the water, then only slows down the tiniest bit more as it enters the beads (which are 99% water). This is why we can't see the beads easily in water. We CAN see the beads when they are exposed to air because the light slows down a lot when it goes from the air directly into the beads. Here is a video where I explain this (and a bit about diapers and baby pee, too. A real life application of the science concepts- I couldn't resist). Sorry for the constant pausing in my explanations- I was giving students the "eye" so they'd pay attention ;)
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The kids were very surprised to learn that in the Science World, the primary colors are different than in the art world! In art, we say the primary colors are red, blue, and yellow. When we are talking about LIGHT, the three primary colors are red, blue, and GREEN! When these colors combine, the results aren't what you'd expect. We did an investigation in class to see what happened as the three primary colors were combined with one another. The quality of the filters on our flashlights wasn't great, but you can kind of see how the colors combined. The kids had the right idea and laid filters over top of one another and we got better results (unfortunately I don't have the video of that). When combined, secondary colors are produced. Red + Blue = MAGENTA (a pinkish purple color) Red + Green = YELLOW Green + Blue = CYAN (a teal-ish color) Red + Green + Blue = WHITE This week we played with flashlights in science. We discovered that light travels in straight paths called rays. We lined up index cards with holes in them to see how the light went through the holes and stopped when blocked. First we reviewed how sound and light are both types of energy that travel in waves. We acted out the difference between the two: sound waves bounce back and forth and light waves go up and down. We also discussed how, unlike sound, light does NOT require a medium (solid, liquid, gas) to travel. Then we investigated light and the visible spectrum. We discovered that the main colors in the visible spectrum are red, orange, yellow, green, blue, and violet. Each color has its own wavelength. The colors in the rainbow occur from longest wavelength to shortest wavelength, with red having the longest and violet having the shortest. We can remember this with the acronym ROY G BV. So how do we see colors? It is all in how light reflects off of objects and into our eyes. In reality, objects don't actually have color! Eyes have special light receptors that send messages to our brains and help us to "see" color. White and black are actually not colors! When we see a "black" object, what we are actually seeing is all of the colors of the visible spectrum being absorbed- none of them are reflected back to our eyes. When these colors are absorbed, the light energy is transformed into heat energy. This is why it is best to avoid wearing black on a hot day- all of the light is absorbed into the shirt and turns into heat! When we see white, what we are actually seeing is a combination of ALL of the colors' wavelengths reflecting back at our eyes in equal amounts. Going back to our black shirt example, on a hot day it is best to wear white because it reflects all of the light and doesn't create excess heat. So now that we know that white and black aren't actually colors, let's talk about why we see colors. Let's use the example of a banana. When we look at a banana, we "see" yellow, but what we are actually seeing is a specific wavelength reflecting into our eyes. Our eyes then send a message to our brains that helps it to interpret the wavelength as the color yellow. So if white light (which we know is a combination of all colors being reflected) is shining on the banana, why don't we see the other colors, too? When white light shines on a banana, all of the other colors' wavelengths are absorbed and only yellow is reflected back at our eyes. There is a great Magic School Bus episode that goes over this in a fun-to-watch way. The episode is called "The Magic School Bus Makes a Rainbow" if you are interested :) You can access it on Safari Montage through our school's library website. In order to see how the colors combine to reflect back in our eyes as white, we did an activity with a circular disc that looked like this: The discs had string tied to them and we then wound the string up tight and released it so the disc would spin really fast in a circle. What resulted was the color wheel spinning so fast the colors seemed to blend together and turn almost white. The colors on the wheel weren't very saturated so some of them turned out looking more brown, but the kids got the idea :) Here are some videos of this activity. Here is a video that shows how to make your own at home if you'd like :) We then experimented and saw in action how black actually absorbs all of the colors! We used something called chromatography to separate all of the colors out of black ink. We drew with a black marker on a coffee filter and then dipped it in water. Since all of the colors separate at different rates, the result of putting water on the black ink was a rainbow of colors. Here are some pictures of the results :) We then mixed all of the colors together into one cup and talked again about how black absorbs all of the colors. |