Archive for the ‘Demonstrations’ Category
Today I had to lecture on the Kinetic Theory of Matter in my Physical Science class. It’s all about how the particles of matter are constantly moving, even in a solid. I came up with three demonstrations that you might want to borrow.
First was discussing the nature of atoms being packed together in a solid. I have a plastic jar of marbles. Students can see how the marbles all nest together in the jar. I gently rattled the jar to have them understand that the molecules (marbles) are in constant motion, even in a solid. I then poured the marbles out into a box lid. I showed how they poured just like a liquid, still took up the same volume, but flowed like a liquid and took the shape of the container like a liquid.
The second demonstration was simple. I lit a match in the corner of the room and we waited while the smell found it’s way across the room to the students at the far end. I used that to talk about how the molecules are moving very rapidly but bumping into one another, so it takes time for the smell to dissipate.
The third demonstration was the best of the day. I put a beaker of water on the overhead projector and let it sit to remove turbulence. I then carefully and gently added a drop of food coloring. Because it was lit from underneath, the kids could see the snake-like tendrils working up and down and on the overhead they could see the color spreading out. After watching for only a couple of minutes the color was mostly uniform. They made me add additional colors and watched them swirl.
I created this lab last night and we did it today. Overall it went fairly well.
I began the lab by lighting a strip of magnesium to demonstrate a chemical change. All that is left after that very bright flare is white powder. They really liked that demonstration. Then on to the lab.
The first part of the lab, students add salt to about 75 or 100 ml of water. I used a tablespoon because it was handy, but that amount seemed to work out well. They stirred the solution until it dissolved, then heated it over a bunsen burner. As the water boiled off, the salt came out of solution and first formed a ring around the middle of the beaker, then formed crystals on the bottom of the beaker. We had to be careful because as the water went away, the salt started splattering. That’s your clue to shut off the gas.
Next, they heated a small amount of the salt in a test tube to see what would happen. There was no physical change, no smell, no color change.
Last, we repeated the above with sugar. Immediately they see the sugar melt and carmelize. The smell is carmel or marshmallows, but it’s not bad. A few of them take it too far, which is good, because you can talk about the sugar becoming carbon and water.
I was very rushed this morning trying to set up for this lab and do everything else I needed to do. I accidentally switched the salt and the sugar, so when the beakers were boiled, I got candy. Except for one group, who didn’t listen and let it go too far. That one turned into a bubbling cauldron of carbon. Great demonstration, lots of smell and mess.
Does anyone know how to get that carbon out of a beaker or test tube? I cleaned for hours today and I can’t get it all out.
I had some fun with the kids today. We first had a discussion about the scientific method, discussing the steps. The classes are just starting their Mythbusters project (check in a previous post), so I wanted them to start thinking. I put out two beakers and let them assume they were both water (one with water, the other was alcohol). On the board was the hypothesis, “We believe the two liquids are different.” I then asked them to come up with ways to test them. I got lots of good stuff; freeze them, boil them, test their acidity, put objects in the liquids, etc. Then I turned the lights out and tried to light them. The alcohol burns with a cool blue flame. They liked that.
Next, I handed out an article on the almost endangered tree octopus. (http://zapatopi.net/treeoctopus/) If you aren’t familiar with this creature, you must read the web page. I did my very best to play this straight and we talked about ways to protect this creature. This went on for a good ten minutes until I finally told them it was totally made up. The point was that they weren’t being critical at all. If a teacher gave them information, it must be true. If it came from the internet, it has to be true. The newspaper and TV are never wrong. They never challenge the information or do any checking on their own.
The last step was that I told them how they can pull a car from the mud by themselves with a rope and a tree. Now they decide not to believe me. They demanded proof. This is my physical science class, so they won’t be calculating the vector forces. Instead, I showed them how it works with a martial arts escape. I have two large kids come up front, each grabbing one arm and pulling opposite. The escape is to take a small step backwards and gently pull them together. The kids will come crashing into each other with quite a bit of force. You have to be careful or they will hurt each other. I then recapped how I gave them a statement, they demanded facts, and I backed the facts up with tangible proof in the form of a demonstration. Finally, they agreed with my statement because it was backed up.
There was a small problem with the printed article. The picture above looks really bad after printing and copying. If I do this again next year, I will put a color picture from the web site on the overhead or perhaps just grab the projector and show the page on the screen.
Trefor suggested a web site that has some really effective simulations: http://phet.colorado.edu/simulations/
I don’t have access to a computer lab, so you won’t see a lot of computer based lesson from me. If anyone has lesson plans to be used with these or any other simulations, I’d love to post them for everyone to use.
The collider at CERN was just turned on this week and the news was all about the possibility of the scientists creating a black hole that could swallow the Earth. Fortunately I’d been doing my reading and was able to talk about how these black holes, if created, would evaporate so quickly that the instruments would only be able to detect them by the residue. This lead to a discussion about particle accelerators and what they do.
I came up with two analogies. The first is the collision of two cars. The vehicles are the atoms, but when they collide, the car is smashed, but we can detect the smaller parts of the car by the bits of headlight and metal strewn about. The collision of the hadrons gives us a glimpse at the world of sub-atomic particles.
A second analogy was an idea for modeling the protons within the accelerator. I grabbed a couple small rare earth magnets from my cabinet and showed how a certain amount of force is required to separate these magnets. The magnets represent the sub-atomic particles. Smaller particles can be separated with a smaller energy collider. To get the bigger magnets apart, we need a bigger collider.
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.
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.
This is an experiment I did in my Conceptual Physics class to demonstrate Conservation of Energy. I take a clean plastic peanut butter jar and put in about an inch of copper BB’s. We then wrap the jar in a towel and have a student start shaking the jar as hard as they can. The towel serves two purposes; it stops the transfer of heat from the students’ hands to the jar, and it helps deaden the deafening sound this little activity generates. Use the non-contact thermometer to take a reading of the BB’s before beginning and then after every two minutes of shaking. I usually set up two or three jars and have the students pass the jar to someone else after the temperature is taken. Chart the temperature on the board. Don’t expect to get anything else done while this is happening. There is too much noise and everybody wants to see how vigorously they can shake the jars.
The students are putting energy into the system because they are shaking the jar. They are actually taking the chemical energy from the food they ate and turning that into kinetic energy. The kinetic energy is transfered into themal energy (heat) because of the friction of the BB’s banging into each other. I just thought of this, but it would be a good idea to have another jar set up as a control.
I love Harbor Freight Tools. If you teach science and have one of these nearby, you must get there. The place has tons of tools at bargain prices. They are made overseas, true, but they warranty everything and I have never had a tool fail on me.
The picture on the right is a digital caliper they sell. I use these for a lab on density and also when we are discussing precision. These calipers work great and they are on sale right now for $7.09. Yes, under $10, try getting something like that from Carolina or Frey or one of the other school lab suppliers.
Another item I purchased from them by the hand full are digital multimeters. Again, from the supply catalogs, expect to pay about $80 for one inexpensive meter. At Harbor Freight these babies go on sale for $2.99. I bought a couple for my house, and even though I have a $100 Fluke meter from my engineering days, I tend to take out my $3 meter when I need a reading. Of the ten or so in my classroom, I’ve had one of the leads break in two years of classroom use. I just bought a whole new meter for another $3 and didn’t worry about it.
Here’s another gem, a non-contact thermometer. I got this beauty on sale for $9.99, and I loved it so much I bought another. These are mine, but I bring them in when I need them for a lab. One day I’ll purchase them for the school, I’ve just been lazy about it so far.
You can find all this and so much more. Here’s a few other items I own and use for school: A dual temperature heat gun for $10 (used to launch hot air balloons), a set of six pliers (electronics sized) for about $5, pulleys, sandpaper, and inexpensive but decent castors in all sizes.
You can look up where your local store is located and all the items including sale items at: www.harborfreightusa.com.
I just found this package through some random surfing. It’s called Phun and it’s a simple graphical world builder with a real physics engine underneath. There is a decent online tutorial and a pretty decent online community to share ideas and solve problems. The download is only 2.8MB, it loads up fast and easy.
Phun can be found here: http://www.phunland.com/wiki/Home
The software was created by Emil Ernerfeldt as part of his masters thesis at Umea University. He calls it a 2D Physics Sandbox and I can see why. You want to take yours shoes off and just play in it all day. Since its creation, Emil has gone to work for a software company where he continues to develop Phun.
Phun is free for an individual to use, but not free for commercial use. Emil made it clear, however, that Phun is free for educational use. I plan to install in on the computers in my classroom and give assignments and perhaps extra credit for designs that demonstrate the principals we are working on in class. There is no reason why my students can’t install the software at home and bring in their creations.
This is a great resource for a Physics or Physical Science teacher. In fact, this book is within arms reach of me as I type this. I would say it is one of the first places I go when I’m looking for a creative new activity or experiment. The cover says it’s for K-9, but I use it with my seniors and find that the labs and activities are just fine.
I referred to this book in my post about the construction of an electric motor using a D cell, wire, and a magnet. The book is a wealth of ideas and I’ve used it as the starting point of an experiment. I mentioned in the other post that there is an updated version that I have not seen.
Summary: Worthy of your shelf space, rated 4/5 Einsteins.
I decided I need to add a book review section to this blog. I have a pile of books that I steal ideas from. This one was on my list to purchase, but I found it in the Juvenile section of our local library. It is written for a budding scientist, but I don’t think it really hits its target. As a teacher, the stuff is almost obvious, so while I got a couple of ideas from the book, mostly it was a quick skim and return to the library. I’m glad I didn’t purchase the book.
Far too much of the book is used to describe examples of simple machines. I spend very little time on machines, so the book isn’t one for my library.
Having said that, I will be looking for his other books at the library in hope of gathering another one or two ideas.
Summary: Worthy of borrowing, not one to purchase. Rated 2/5 Einsteins.
This is a trick that most real woodworkers know. When you need to replace the handle of a tool, you put the head of the hammer on the handle and then you drive the head down by holding the hammer vertically and hitting the bottom of the handle on a concrete floor. This is also how you tighten the fit of the head on the handle.
Because the head is heavy, the downward inertia of the head causes it to continue down, causing it to tighten itself. I have an old hammer head in my shop that I’m going to purchase a handle for, just to demonstrate this principal.
Do I really have 517 demonstrations of inertia? It feels that way, but of course I don’t. I max out at around 300. Anyway, this is similar to putting an anvil on your stomach and then hitting an anvil with a sledge hammer. I’m just not that trusting. Here’s how I made it safe for High School seniors:
I take a box of books. I have a case of Conceptual Physics books, they weigh about 80 lbs. I have a student come up to my demonstration table and lie down. I like to pick one of my more vocal (translate as annoying) but also smaller in frame kids. They lay on their back and I gently place the box of books on their chest and stomach. When they agree they are not in pain, I usually call up the biggest and strongest kid in the class. His job is to slam his fists down on the box of books as hard as he can. This is usually a friend of the one laying down, so the drama is even better.
As hard as he hits the box, the kid on the table barely feels anything. While he’s still there, I ask them about removing some of the books from the box and what do they think would happen. I like for them to take the thought experiment to the extreme, so I ask if we take all the books away and replace it with a single piece of paper. Then what would happen? My hope is that they see how the large mass has a lot of inertia and resists a change in motion.
This usually moves to about half the class trying this on each other at my table. Chaos, you bet, I encourage it. They are interested enough to get out of their chairs and try an experiment, you better believe I’m going to let them. I’ll take every teachable moment I can get.