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A collection of helpful articles on teachers and teaching

Black Boxes

I always tell my students that all of chemistry is guided by those pesky little electrons. Since you cannot see them it is tough to teach kids about how them. All of the evidence you can present is indirect. So, I start with indirect evidence.

The classic Black Box Lab:
I take a box and place an item inside. The item is usually a paperclip or marble or something that the student would identify on sight. I allow the students to examine the box and try to find out what is inside using any technique except opening the box. They tilt and listen, use magnets, and shake the box to try to figure out what is inside. I ask the students to record their tests and observations. We spend a lot of time talking about the nature of their evidence. Older students will figure out that they are using what they know and have experienced (how a marble rolls, the shape of a paperclip) to identify the object. This assumption that processes we see will be similar for items we can only examine indirectly is a big part of science. It does not always work for things as small as electrons (quantum rules) but it is how we approach and understand the world we cannot see like atoms. To really frustrate the kids try not letting them see the object inside the box. It is not a cruel twist of teacher power but a closer approximation to how science works. Scientists can only do more experiments when they cannot see an object.

So, now the kids know that indirect evidence is pretty powerful and that it is a cornerstone of science. What indirect evidence of atoms and their behavior can you see in a 55 minute period?
I begin with scotch tape. I take two 10 inch pieces of tape slowly off the roll and hold the pieces together. On a dry day they should repel as they are charged the same. Now, I place one piece of tape sticky side down on a desk and rip it off quickly. When I do this some of the electrons come off too and now this piece of tape is charged a little on the positive side and it will be attracted to the other piece of tape. There is a physical science explanation and more instructions for this at:
http://narn.physics.auburn.edu/etjr/teaching/phys1000-S07/labs/exp12.pdf
 
There is a non-profit organization called RAFT (Resources for Area Teachers). They use recycled materials to make some of the most amazing activities. Their web site is one of my all time favorites for great labs. Make sure you check out their idea sheets.
http://www.raft.net/index.php?pg=main

The all time favorite static electricity activity is the balloon on the wall. You can rub a balloon on your head and the balloon will “stick” to the wall using the forces of the electrons you rubbed off. Take this a step further and you can use that same principal to move pop cans. You can use some plastic wrap to charge up a pop can and then use the balloon to see if it is attracted to the balloon or repelled by the balloon. This is a great time to get the problem solving juices flowing and ask the kids to give you an explanation of what is happening. What could have fewer electrons? What do we mean by attraction and what is repulsion? I ALWAYS ask the students to back up their thinking with evidence.

Once again the Exploratorium has a great description of this experiment:
http://www.exploratorium.edu/science_explorer/roller.html
 
A good explanation of static electricity and the connection to atoms can be found at this web site:
http://www.sciencemadesimple.com/static.html

The big finish is a large thin piece of wood.  A meter stick will work but it is better if you have something really longer like a piece of 1×1 wood or thinner. You place the middle of the wood on something that will allow it to spin on a table. I use a watch glass but a pencil or marble or even round crumpled ball of paper will work fine. I take the balloon and charge it up by rubbing the balloon with a piece of wool. Then, holding the balloon near the wood the wood will begin to spin. The larger the wood the more spectacular the effect.
So, as the heat comes on and the air turns dry it is a good time to take a look at indirect evidence and use some static electricity to get kids thinking about those tiny little particles that make up our world.

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