Archive for October 2008
Today my Physical Science classes did two short labs in one period. Both of these mini-labs came from the book “Super Science with Simple Stuff!” by Susan Popelka. The book is geared towards middle school, but that never bothers me.
The first was using air pressure to crush a soda can. I was going to do this as a demonstration, but when I tried it this morning, the impact of the event was so powerful, I decided to have the kids do it themselves.
What you do is take a soda can and put about 1/4″ of water in it. Heat the can over a bunsen burner until the water is boiling. If you have a triangle support on a ring stand, it takes about one minute. If you have an asbestos wire mesh, it takes a couple more minutes. When the water in the can is boiling, use tongs and invert the can into a bowl of water. The can implodes instantly and dramatically. I’m a jaded science geek and it impressed me. The kids absolutely loved it. I had extra cans so they could do it again, they used up all my cans in both my classes.
The second lab uses Corn Syrup, Water, Vegetable Oil, and Rubbing Alcohol. I used a 250ml beaker and had them put 50ml of each liquid. First the corn syrup, then the water. Before adding the water, they added a drop of blue food coloring. Next they added the oil, but poured it over the back of a spoon so it would cause the layers to mix. Last the alcohol with a drop of red food coloring, again poured in over the back of a spoon. You get four very distinct layers. Then use random items to see if they float in between the layers. I used wooden toothpicks, bits of a plastic spoon, beans, and bits of Styrofoam from a cup.
The kids all commented how cool the lab was today. They enjoyed it and were really excited.
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 know this outside of my usual posting, but when I saw this I just wanted it. No, I won’t be bidding, it’s a bit out of my price range.
Here’s the eBay link:
On the eBay page, you can see the inside page with the signature. The starting price is $1000 and they are estimating it will sell for between $2000 and $3000. I think it’s worth $1000, but I’m a little short on cash this week.
If any of my students are looking for a Christmas present for Mr. Physics, I have the perfect item right here.
Epilog: The link is still live; the book went for a mere $1000 and there was only one bidder. I could have been a contender. Damn.
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.