We talked a little about the number pi: it's an irrational number meaning it will go on infinitely without repeating. So far, mathematicians have been able to use super computers to calculate more than two billion digits of pi. This long strand of digits actually made pi fit in nicely with today's lesson; polymers also form long strands.
In case you're curious, here are the first million digits of pi.
http://www.piday.org/million.php
We talked about how we use pi to find the circumference and area of a circle. The circumference is pi multiplied by the diameter while the area is pi times the radius squared. You will end up with pi any time you divide the circumference of a circle by its diameter. It does not matter how big or small the circle is.
Pi Unrolled animation:
http://commons.wikimedia.org/wiki/File:Pi-unrolled_slow.gif
More information on pi:
http://www.historyforkids.org/scienceforkids/math/geometry/pi.htm
http://www.faqkids.com/161-what-is-pi.html
March 14th is also Albert Einstein's birthday. He was born on March 14th, 1879. We spent a little time talking about Einstein. He was awarded the 1921 Nobel Prize for Physics and, in 1955, the 99th element of the periodic table, Einsteinium, was named after him.
More information on Albert Einstein:
http://www.biography.com/bio4kids/bio4kids-einstein.jsp
Polymers
Polymers are really quite fascinating. We encounter them on a daily basis but may not know it. As simple as that plastic bag or piece of PVC pipe may seem on the outside, the chemistry of those objects is pretty complex.
We've looked at the periodic table several times in this class. Each of the symbols stands for one atom on that element. So, if we just wrote down H, it would stand for one atom of hydrogen. Atoms can join with other atoms to form molecules. That one atom of hydrogen could join with another atom of hydrogen to form H2, one molecule of hydrogen. If we added one atom of oxygen to that molecule of hydrogen, they would form H2O or water. I drew pictures on the board to show these bonds.
Water is a relatively small molecule but some molecules are really big. Vitamin C, for example, is written as C6H8O6. That's 20 atoms! I drew a vitamin C molecule on the board and then told the students we could move those 20 atoms around a bit and, while we'd still have six atoms of carbon, eight of hydrogen, and six of oxygen, it would not be vitamin C. How molecules are bonded determines how they act and react. We'll get into chemical reactions more next week.
A polymer is a chain of many molecules that join together. Scientists call each of those molecules monomers. I wrote the words polymer and monomer on the board and explained that mono means one and poly means many. Some polymers are linear polymers meaning they join together to form a long chain. Others are branched polymers; these have a chain with lots of branches coming off it.
Types of polymers
Polymers can be natural or synthetic. Natural polymers include rubber; starch; glucose (the sugar formed by plants as a product of photosynthesis); wood; chitin (found in the shells of shellfish, exoskeletons of bugs, and the cell walls of mushrooms); and proteins in foods as well as your skin, hair, and fingernails.
Synthetic polymers often come in the form of plastics. These include PVC (polyvinylchloride), nylon, Styrofoam (polystyrene), polypropylene (#5 plastic), and polyethylene (#2 plastic).
Click here to see how monomers join together to form polymers.
Teflon (used to make non-stick coating for pans as well as thread-seal tape for plumbing) is known as polytetrafluoroethylene or PTFE. Even Kevlar is a synthetic polymer.
Polymer labs and projects
Expanding Gummy Bears
Gummy bears are made with gelatin, a natural polymer. This lab showed diffusion, the movement of water into another substance.
I had two gummy bears that I soaked in water overnight. One was soaked in regular tap water; the other sat in distilled water. Each student was given one dry gummy bear and asked to measure it. We found that a new, dry gummy bear measured about 1 1/2 cm. We then measured the gummy bears that had been soaking. Diffusion caused the bear from the distilled water to expand to 3 1/2 cm while the bear that had been in tap water expanded to 3 cm.
Balloon Trick
The students used a bamboo skewer to pierce a balloon without popping the balloon. They inflated the balloons then used cotton balls to dab a little veggie oil on the dark spot at the top of the balloon. This helps the skewer go through the rubber. The students then applied just a little pressure while twisting the skewer. Most were able to get the skewer into the balloon.
If you like a challenge, try getting the skewer all the way through the balloon and out of the bottom of the balloon.
Ooblek
Ooblek is simply a mixture of cornstarch (a polymer) and water (1 part water to 2 parts cornstarch). You can add a few drops of food coloring if you like.
The fun thing about ooblek is that it is a non-Newtonian fluid (a dilatant) that has properties of both solids and liquids.
Non-Newtonian fluids
Fluids are substances that can flow. They have a property called viscosity which describes the thickness of any fluid and its resistance to flowing. Sir Isaac Newton believed that the viscosity of a fluid could only be changed by changing its temperature. Those that change viscosity due to temperature changes (water, oil) are Newtonian fluids. However, you can change the viscosity of some fluids by applying a force. These are the non-Newtonian fluids. Pushing or pulling on the ooblek changes its viscosity.
Fake Snow
Our fake snow looked more like slush but it was still fun to make!
The students mixed a polymer called sodium polyacrylate with water. Sodium polyacrylate is known as the "diaper polymer" since it's used as an absorbent material in disposable diapers.
Bouncing Polymer Ball
I think we needed to make a bigger batch of this to make bouncy balls with. The stuff we ended up with was not enough to form anything with. It did make a nice slime material, though!
The students mixed 2 tbsp. of warm water with 1/2 tsp. of borax in a cup. We poured 1 tbsp. of school glue into a separate cup then mixed 1/2 tsp. of the borax mixture into the glue. The students added 1 tbsp. of cornstarch to the glue-borax mixture and stirred well.
Doubling the materials used would probably be enough to create a ball. Just mix until it becomes too stiff then pull the mixture out of the cup and mold it into a ball shape with your hands.
Here is the history of Silly Putty:
http://chemistry.about.com/od/everydaychemistry/a/sillyputty.htm
Next week:
Chemical reactions and solutions.
References:
I found lots of information about polymers on The Kids' Macrogalleria site. The Expanding Gummy Bears idea also came from this site.
There is so much more information that we didn't get to. I could spend weeks on this topic!
I found the Ooblek recipe here:
http://chemistry.about.com/od/chemistryhowtoguide/ht/oobleck.htm
The Fake Snow recipe came from this website:
http://chemistry.about.com/od/chemistryhowtoguide/ht/fakesnow.htm
You can learn more about the bouncing polymer ball project here:
http://chemistry.about.com/od/demonstrationsexperiments/ss/bounceball.htm
Remember these from last week?
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