Wednesday, March 19, 2014

Oobleck & The Butter Battle

For Read Across America Day, which is held annually on Dr. Seuss' birthday (March 2nd), students connected their literacy and science that day by making what they read about in his stories come to life.

In Mrs. Fielder's classroom they read Bartholomew and the Oobleck. The story describes the adventures of Bartholomew as he watches the King of Derwin order his royal magicians to create storm that will drop a different substance to fall from the sky than the normal rain, snow or fog. This substance is a very sticky substance called Oobleck and it gets into just about everything in the kingdom and life as they once knew it was completely in interrupted because they are stuck to the Oobleck. The falling blobs of Oobleck eventually start to get so large that eventually everyone gets stuck in it and cannot escape. The king tries to make the storm go away by changing magic words but Bartholomew tells the king he just needs to say sorry to the sky. Once he does, the sun comes out and melts the Oobleck away freeing all the citizens of kingdom. Mrs. Fielder's class first wrote a hypothesis based on what they read about in the book to predict what Oobleck would look and feel like. Next, then they followed a recipe to make it themselves. After having time to explore and make observations, they concluded by comparing their original hypotheses to their observations and discussed if they thought Oobleck was a solid, liquid, or a gas. Most students agreed that they thought it fit best as a liquid because it could be poured.

Here is a picture of the students mixing their Oobleck. If you want to try and make it at home, follow the link to Scientific American's Home Activity. They not only have the recipe there but also a nice video clip that walks you through how to make it as well as some fun things you can do with Oobleck. Oobleck is similar to the bouncy balls in that it is considered a Non-Newtonian fluid which explains its strange properties. For more on this, look through the blog on the bouncy balls.

In Mrs. Christopherson's class, they read the book The Butter Battle Book.  The battle at the center of this book is between the Yooks and the Zooks who are separated by a large wall (not too different than the Berlin Wall) because they butter their bread on opposite sides. The disagreement leads to an arms race where they are sure to destroy one another. The arms race starts with slingshots, progresses to guns followed by airborne copters to drop goo on their enemies, ending with the creation of bombs which neither side can defend. The book ends with the generals of both sides poised to drop the bombs on each other and leaves the reader to decide what might happen. To see what this dispute was all about, students made butter themselves by shaking it in a jar and following a simple recipe. Here is a link to a similar recipe and process used in class from PBS Kids Zoom. You can do this at home with your children as well and they can post their results on the website and read about what happened when other people tried this around the country. Once they made the butter, they got to spread it on the top and bottom of a piece of bread and then they collected class data to determine which tasted better and made a graph, just like in the book. Deciding if the butter was a reversible change sparked a heated debate in their classroom. Most students agreed that it could melt back into a liquid but some were bothered because they didn't think it could turn back into the cream it started as. Turns out the kids were exactly right! Since butter is made by causing all the fat in cream to stick together during the shaking or churning process and you poured the liquid off, it cannot be restored to its original cream state but when exposed to higher temperature the fat will soften and eventually melt into a liquid. Here are some pictures of the students buttering their bread for the taste test.

I scream, you scream, we all scream for ICE CREAM!

Student continued with their recipe books by making ice cream in class. This can be done at home with a simple recipe and ingredients you likely already have. Here is a similar recipe to what students used in class: Make Ice Cream in a Baggie. The basic idea is that you put all the ingredients in the smaller baggie and then place it inside the large baggie with salt and ice. Now you, "shake, shake, shake" until your ice cream solidifies and then you can take it out and reap the benefits of all your hard work. I have done this activity myself many times and one thing to remember is that you want to rinse the lip of the small baggie with water before opening it to eat your ice cream. If you don't, you will have salt water fall onto your ice cream and it won't taste so good. This is a perfect activity to save for a hot day when everyone needs a fun activity that will lead to cooling down in the end.

Here are some pictures of the ice cream:

Is this change reversible or not? The students definitely thought that the ice cream would melt back into a liquid and that would be reversible. Interestingly, they didn't mention if they would be able to recover all the initial ingredients separately. They were convinced with the bouncy balls that they wouldn't be able to return it to glue and cornstarch although they didn't really seem to consider if they could get the vanilla, milk, or sugar back. This is a solution of many ingredients but since they are dissolving and there are no chemical bonds formed during cooling, it is a reversible change. It would be difficult to recover the ingredients separately from one another when back in the liquid state. It would be interesting to challenge your student to come up with a plan of how they could separate this mixture. Could they boil some off? What would that leave behind? Could they use a filter and a funnel? What would that leave behind? What are other separation ideas they can come up with? Since milk is a solution of fats, sugars, and water will their methods separate this out as well?

The reason the ice cream solidifies is that by adding salt to the ice in the larger baggie, you lower the freezing point of the ice. This is called freezing point depression. Normally, water freezes at 32 deg F or 0 deg C but when we add salt, it causes it to freeze at a lower temperature than that. This is also why we throw salt on our sidewalks or on the road when it snows, by lowering the freezing point but keeping the same temperature outside, the snow melts and turns back into its liquid form. How much lower the freezing point will become depends on several factors, the concentration of the solution of salt water being one. So if you give ice cream a try and are having a tough time getting it pretty solid, one thing you can try is adding more salt next time to see if you can get a different result!

Phases of Matter Brain Frame & Homework

Students in Mrs. LeCarno's second grade class did a categorizing Brain Frame on the phases of matter. Each student had a description of either a solid, liquid, or gas and needed to bring it to the grid and explain why they thought that description fit best under one of the three phases of matter. Having students explain why the description fits in one category or another gives them an opportunity to work on using their academic vocabulary and discourse with one another. In the first grade, they adapted this activity to do as a group and also used it as a way to identify facts from opinions, which is something they are working on for Language Arts. Mrs. Christopherson would read the description and then students first had to decide what phase of matter it belonged to and then additionally had to decide as a group if it was a fact or an opinion. They explained why some statements were facts by citing evidence that they could to observe, measure, or prove the statement. An opinion was noticed when it was debatable, which students explained as people having differing opinions on the statement.  This activity sparked great conversation and debate among the students and also the idea surfaced that if the substance is moving fast then it must be a gas. The students were having a difficult time separating the movement of the substance with the movement of the particles in the substance. They resolved to come back tomorrow and explore this idea a bit more with additional examples.

A great way to see the difference between the movement of the particles is to use the University of Colorado's PhET Simulation Phases of Matter. It will allow you to "see inside" a substance to see that even particles in a solid are moving but as you raise the temperature they move more and more, eventually they gain enough energy that the bonds holding the particles together in the solid phase are broken and it transforms into a liquid. Weaker forces hold liquids together but as you keep increasing the energy, eventually enough energy will be absorbed to overcome the attraction between the particles and allow them to fly apart in a gas.

Students also had to go home and find substances in their home that were solid, liquid, and gas and bring them back to class. Here are some of the examples that were brought in:

You will notice that all the students have water or a substance that is mostly water as their liquid and air as the gas. It is challenging to find examples other than these around the home but I would encourage you and your children to research some other less common examples so that they can come to understand not all liquids are water and not all gases are air.

Tuesday, March 18, 2014

Bouncy Balls

Students in the first and second grade have now started to make their recipe book portfolios. Each couple of days, students are investigating a new change in matter and studying it to see if it is reversible or not. They began by making bouncy balls in class following a simple recipe with home ingredients you likely already have around the house.

Follow this link to find the recipe for making bouncy balls at home: Bouncy Balls

The glue is a long chain polymer called polyvinyl acetate that looks something like this:

The small "n" in the diagram is showing you what the repeating unit in the chain, otherwise known as a monomer,  looks like. You see that this chain has two repeating units but glue is made up of chains that range anywhere from 100 to 5,000 units. The R's at either end represent the chain expanding out in either direction. When we have a long chain of repeating units it is now known as a polymer.

When mixing the ingredients together, a chemical reaction occurs that causes the borax to make additional bonds between glue chains and within them, known as cross-linking, in lots of places causing the molecules to fold in on themselves. This is similar to how a protein is folded after it is made to make it functional in your body. As the molecules pull closer together as stirring proceeds a glob or ball starts to appear which can be removed and rolled. Once it has dried out it will become more "bouncy." Students are focusing on wether a change that they observe is "reversible" or not. Due to the cross linking and the formation of additional bonds, the making of the ball is not a reversible change. Students did observe that if they left their ball on the table for a period of time it became flat and that it was easy to roll it back into a ball again. This is a reversible change because it was only a change in appearance.

Here are some pictures of the bouncy balls that students made. Since they used Elmer's glue their balls are opaque. You can also use clear or blue glue to make yours translucent. Adding food cooling makes each student's product individualized.

Questions to ask you student about this experiment:

  • What did you observe happening while you were making the ball?
  • What did the ball feel like as you were rolling it?
  • What happened to your ball if you set in on the table and walked away for a while? Is this change reversible or not?
  • What does the ball look and feel like now (two weeks later) compared to when you first made it?
  • Is your bouncy ball a solid, liquid, or a gas? How can you tell?
  • Is the change that happened to the bouncy ball reversible or not? How do you know or how can you find out?
  • How could you change the ratios of the ingredients to make it bouncier or less bouncy? More or less sticky? Give it a try at home!
The answer about wether it is a solid, liquid, or gas is actually a tough question. These globs are actually what is considered a Non-Newtonian fluid, meaning sometimes it acts like a liquid but it doesn't follow all the rules we traditionally use for a liquid and sometimes it acts like a solid. Students are using the fact that liquids flow or run when poured as evidence that matter is in the liquid state. If you imagine a fluid as several layers sliding past one another, Newton thought that tif you wanted to force the layers to slide twice as fast past one another that the force resisting the flow would be twice as great. Unfortunately, not all liquids follow this rule. Non-Newtonian liquids are ones where the resisting force is more or less than double the amount of resisting force. Not only are the bouncy balls an exception to this rule but ketchup, blood, and yogurt are a few other examples. When Non-Newtonian liquids are stressed by a sudden rip, tear, or shake they can act more like a solid.