Archive for August 2008
Let’s start off with the theory. Water has more of a positive charge on one side and a negative charge on the other. This is because of the way the molecules bond. The picture on the right shows the Mickey Mouse structure of water molecules. Oxygen has six electrons on the outer shell and wants to have eight. So it uses the electrons from the Hydrogen atoms to complete its shell. I’m not a chemist, I don’t know why the molecules make a Mickey Mouse and don’t spread out onto opposite sides, but they don’t. The result is a net positive charge near the ears and a negative charge on the other side.
There is a really cool and simple demonstration to show the polar nature of water. Turn on the faucet so that you have a laminar stream of water coming out. Alternatively, you could set up a simple apparatus that controls the flow of water from a flask. You want the stream to be a small as possible but still laminar (flowing in a parallel stream with no turbulence). Now charge up a plastic rod or a comb or anything that will hold a static charge (even a balloon rubbed on your hair will work. Put the charged object near the water and the stream will deflect. This freaks the kids out. I love freaking the kids out.
This is a standard demo, one I did with my 8th grade Physical Science class and it stuck with them. It uses sugar to show the difference between a physical change and a chemical change. The first step is to dissolve sugar in water and then evaporating the water over a low flame. I usually use a beaker over a burner. The sugar will crystallize out and can be dried and returned to its original form.
The second step involves heating sugar in a test tube until it carmelizes and turns to carbon. The kids smell the change and associate the smell with a property change. We try but can’t get the mess to turn back into sugar.
If you haven’t done this before, don’t go by the picture, it’s just a photo I found on the web. You want to gently heat the test tube with the sugar. You only need a small amount of sugar (1/2 at the bottom of the test tube) and if you do it slowly and carefully, you will first see the sugar melt and then start to change. Gently waft the odors to the students as it starts to change. If you go fast, you will stink up the place. I often hold the test tube in my hands as I heat the bottom. It doesn’t get hot if you go slowly.
I usually throw the test tube out, it’s just not worth cleaning it once the change takes place. If someone knows how to clean it easily, please comment. Thanks.
I just got this idea in the shower this morning. Here’s the basic lesson:
- Divide the class into groups. Give each group a complete but non-working flashlight.
- Ask them to look at the flashlight, but not take it apart. They are to predict why it isn’t working and propose a solution. They need to come up with a test to show their prediction is correct.
- Once documented, they can take the flashlight apart and attempt repairs.
- Each time they reassemble the flashlight and it doesn’t work, they need to stop and come up with a new written plan.
- The group must document each step as they try to determine what is wrong with their flashlight.
Since these are very simple devices, they can be set up as follows:
- One or more dead batteries
- Tape over battery terminal
- Batteries installed incorrectly (positives together)
- Dead bulb (see update below)
- Switch or broken circuit in flashlight
I would probably set each flashlight up with at least two failures so that the exercise is not over in a minute. For instance, if I installed the batteries incorrectly, I would also make sure that one of them is dead.
There are two ways they can problem solve. They can share parts with other groups to make the flashlights work or there can be a pile of batteries, bulbs, and bodies to use. I’m also not sure if I want to have meters available. I may have them available but only if someone thinks to ask for one.
I’m not sure how I want to conclude the lesson. I would probably go into a class discussion of how they developed their plan and made sure the test did what it was supposed to do.
This looks like it’s going to be fun to watch. I need ideas for wrapping it up.
Update… We did this lab today (9/11/08)
I wrote a lab procedure for this: Flashlight Lab. There were only a couple little changes. I used clear plastic between the bulb and the bulb holder. It made the bulb look perfectly normal, but it formed a nice invisible insulator that served to fool them for quite a while. For the switch, I put clear tape over the contact from the switch. Some of them found that though, it was hard to disguise and it stood out.
I didn’t let the students share information between groups. I told them I didn’t have spare batteries, so they had to come up with a way to test them. If they were clever enough to ask, I let them use a multimeter or spare parts from other flashlights. I didn’t show them how to use the meter, but I did set it up properly. They figured it out on their own, which impressed me. I was hoping they would think of swapping parts with their neighbor, but they didn’t.
This lesson served two purposes: it demonstrated the scientific method since they had to cycle through the hypothesis-test-results process several times until they figured out everything that was wrong. The lab also served as a lesson in following directions. One of the groups did exactly what they were to told not to do and took everything apart and got it working in a minute. They had no documentation, hypothesis, or controls. They couldn’t tell me the three problems with their flashlight, their experiment was worthless. I told them that they failed the lab and they also showed me I can’t trust them with chemicals and fire in the lab if I can’t trust them with a flashlight. Hopefully that made an impression.
This experiment was done in my 12th grade Physical Science class and the overall response was positive. The kids liked the hands-on challenge and were impressed at how devious I was at sabotaging the flashlight. I think this is definitely worth doing. Let me know what you change and improve.
This is an interesting video I found somehow. I seem to be surfing a bit too much lately. Actually, I don’t surf, I Stumble! Yeah, you know what I’m talking about.
Anyway, this video uses animation of magnetic field lines to enhance live video. The result is so realistic I’m worried my students will think this is something we can see with the right kind of filter.
Take a look for yourself and give me some feedback.
A friend of mine who teaches Middle School Technology gave me this catalog a couple of years ago. There is actually a series of catalogs for different areas. Their web site is a bit confusing, it seems they are a series of companies, all with the goal of improving technology and science education.
The “PITSCO Ideas and Solutions” catalog is a perfect fit for this web site. The catalog is organized into activities such as Robotics, Sustainable Energy, Physical Science, etc. Under each subheading is one or more activities. Under Physical Science, they have kits and materials for Mouse Trap Vehicles, Catapults, Trebuchet, and Egg Drop Vehicles.
I really like their ideas, and there are a lot of them, but they seem totally focused on Middle School. The materials are very expensive and can often be easily found for much less money. For instance, you may have read my post about building Hot-Air Balloons. They have a material kit that has enough tissue paper, glue sticks, etc to make 25 balloons for $99. I’m pretty sure you can do that for less than $20 with no difficulty. They have a propane burner launch station designed with safety in mind for $345. Don’t get me wrong, great stuff, just pricey.
You can find them on the web at www.shop-pitsco.com. I suggest you start by ordering a catalog.
I’m just getting started, there is so much to add to the site. I really need to rethink the categories and tags and go back and then update all the posts. I want to thank those of you that wrote me, I really appreciate the kind words. The amount of traffic tells me this is a useful site for other science teachers. It’s two months, I’ve had over 4400 pages views, and that’s without a single nude image.
I’m still in need of collaborators. There is so much I don’t know and so many clever and creative ways to teach Physics and Physical Science. But even if you don’t post or author anything, feel free to use and modify anything you find here.
Here’s my prediction – 8000 page views by Sept 1, the three month birthday. Thanks for stopping by.