Slurping Rainbows

Jelly Marbles 2013

Students who deal with Mr. Ramsey learn sooner or later that one phrase he will not tolerate in his classroom is “That sucks.” Something about it just sets his teeth on edge. There is one exception, though. As the Explorers learned during a session in February, there is a type of material that truly DOES suck, and in a seriously impressive way.

The students experimented with (ah, shoot, let’s call it what it is—we PLAYED with the stuff) several materials that looked different but all shared one common characteristic. Each of them is what is known as a “super absorber,” meaning that they can soak up a huge amount of water compared to their own mass. This gives them some interesting properties.

The first material the group checked out is known as “instant snow.” It starts off as a fine white powder, but when a cup of water is poured onto it the powder quickly absorbs the water, becoming a white fluffy material that feels suspiciously dry. In short, it feels and looks just like snow—warm snow, granted, and snow that shows no inclination to melt, but snow nonetheless. The first question was “Where did the water go?” The answer is that it didn’t “go” anywhere—it is still present, but the water molecules are now locked up inside the linked molecules of the instant snow. As the students recognized, this is a bit similar to how the water gets trapped inside the slime that we made earlier in the year, although the chemical processes involved are very different.

Mr. Ramsey explained to the students that if the “snow” is left alone long enough (say, several weeks), the water molecules will slowly manage to escape and evaporate, leaving the powder behind. And then the whole process can be repeated—add more water to the powder, and poof, more instant snow. (The students were also thrilled to learn that what they were playing with is basically the same stuff that is found in disposable diapers—a situation where you really do want a material that can soak up lots of liquid and still feel dry!)

Next the Explorers looked at another substance made of the same basic material but with a different appearance. Well, actually it would be more proper to say that they “felt” this substance to begin with, rather than actually seeing it. This stuff starts off as tiny hard crystals, but when dumped in water the crystals swell up into round, clear, squishy balls about a centimeter across—essentially the size of marbles, giving them the name “jelly marbles.” They are plenty fun to play with just on their own, but their true revelation comes when they are dropped back into water—they disappear!

This invisibility trick happens because of “refraction,” which is the bending of light waves. As light passes through different materials (glass, water, air) it speeds up and slows down, making it bend as it goes from one material to another. You can see this when you look at a coin in a pool that isn’t really where it seems to be, or if you notice that a spoon in a glass of water seems to be broken where it enters the water. This effect also explains why you can easily see a regular glass marble inside water, even though both the marble and the water are “clear.”

The jelly marbles, however, are made almost entirely out of water themselves after they swell up, so light passing through them behaves exactly like it does when it passes through the water itself—so no bending and therefore no visibility. You can FEEL them, though, even if you can’t see them—which as the students discovered for themselves can be a slightly creepy experience when you reach your hand into a big bowl that you think has nothing but water in it! Once you pull them out of the water, they are easily visible, since the light refracts as it passes from the air and through the jelly marbles.

The last material the students investigated is actually the same stuff as the jelly marbles, but without the round shape and with coloring added. These “jelly crystals” come in three colors—red, blue, and yellow. Each pair of students got a bowl of each color with instructions to put them into layers inside an empty water bottle. Once the bottles were filled up we capped them off tightly to prevent the water molecules from evaporating. Mr. Ramsey told the students to take these creations home and watch them over the coming days—over time, the colors from crystals that are touching one another will “bleed” together and mix, creating a rainbow effect throughout the bottle. Even this will pass eventually, though, as the colors will continue mixing until the entire bottle is one uniform color—something of a darkish purple, if past results hold true.

Check out the photo gallery to see pictures from our sucky day. Click on the links below for more information on these super absorbers and for previous activities with the same materials, or for a place you can buy the materials to play with at home.

Earlier Jelly Marbles

Buying Jelly Marbles

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OH - Dayton / Wright-Patterson Air Force Base

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Reported on:
Sat, 08/20/2016 - 09:08