This experiment came from Diane in South-central Pennsylvania. She and her son were discussing ceiling fans, and how they make you feel cooler. They wanted to know if the fan actually cools the room, or does it just feel that way?
This experiment is the result of my forgetfulness. I took a tray of ice cubes out of the freezer, used half the cubes and then forgot to put the tray back in the freezer. When I remembered, the cubes were half melted. Only the centers of the cubes were left, and that ice was very cloudy.
Quite a bit of my travels involve changes in altitude. Going from sea level to over 7000 feet makes a big difference. As you go higher, the air pressure is less. This can do bad things to the stuff in your suitcase, such as causing shampoo to squirt all over your clothes. It would be nice to fly all of you up into the mountains to do this experiment, but I can't quite afford that right now. Instead, we will cause a change in air pressure by heating and cooling it.
One of the most common questions that I get is where do I get the ideas for these experiments. Some are old classics that I try to give a new angle. Others are the result of questions sent to me by subscribers. Some of the ones that I like the best are the ones that just pop up, seemingly out of nowhere. This is one of those. It also comes with its own story, which makes it even better.
The story is one of Aesop's fables. If you have never read any of these, go read some. It is well worth the time.
This week we had a marvelous electrical storm to the west of our house. It was far enough away to make Junie Moon the Dog happy, but near enough for some nice photos. Since it was night, I used the same settings that I use for star photography. I put my Nikon D7000 on the tripod, with an 10-70mm lens. I set it for manual exposure, and set the shutter for a 30 second exposure, and turned on long exposure noise reduction. I hooked up my PClix, a marvelous device for taking photos at set intervals. Then I just let it click away.
I love it when teachers ask questions! I alway enjoy a good science question because they make me really think about the subject to be sure I give the right answer, but when a teacher asks a question, I feel obligated to give an answer (if I can) that will let them explain the subject to their students. Recently, I have been talking with a teacher friend, about chemical and physical changes, and the more we talked, the more I thought the rest of you might find this useful.
I mentioned that I had a lot of fun experimenting with carbonated soda (and drinking it) and that I should do an experiment with chocolate. I got quite a few e-mails suggesting experiments with chocolate, but this one was the most common. It has to do with the white discoloration that you sometimes find on old chocolate.