We started class by watching some videos on youtube, mainly slow motion videos of water balloons popping and the Amoeba Sisters video explaining how the special properties of water, like surface tension are due to the polarity of water molecules.
After the movies the kids floated paper clips in a glass of water. They had to be careful putting them on the surface or they would sink. Then they used disposable pipettes to see how many drops of water they could put on a penny before it over flowed. They repeated the same experiment with isopropyl alcohol and saw they got fewer drops to stay on the penny. And finally they saw that detergent could break the surface tension on the pennies and make the paperclips sink in the cup. Here are some slow motion videos we took today.
Slow motion movie from class of isopropyl alcohol drops on penny already covered with isopropyl alcohol.
Sticking a toothpick in a big water drop on a penny.
Breaking the surface tension with a toothpick dipped in dishsoap.
The activies we did today are described in Chapter 5 of the Middle School Chemistry curriculum by the American Chemical Society and you can also see them in Physics Girl’s video below.
I highly recommend doing the milk one at the beginning. Its a lot of fun.