When my son was two years old he played a horrible game we affectionately called "sink or float". He would grab a little toy or my make up, or a book...anything his little hands could find. Then he would run as fast as his little legs could carry him to the bathroom. Upon hearing his rapid tiny footsteps, my husband or I would jump up and chase him as fast as we could. That is because we knew what he was going to do next...throw that item into the toilet to see if it would sink or float.
We look back at this now and laugh, but I do not miss that game. Today he is quite grown up, but his mind is still as curious as it was back then. I find myself coming up with fun science experiments that can challenge him to test his theories and ideas.
Years later I find that my boys are still fascinated by playing with water and seeing what things can sink or float. They had all kind of questions. How do bugs walk on water? Why do ships float, but metal sinks? How do submarines dive and surface?
I decided to show them how water pressure can affect where an item is in the water. In 2016, they made their first Cartesian divers. In the photo above you can see the intense look on my middle son's face as he squeezed that bottle to make his diver sink and float in the water. If you have never made a Cartesian diver with your kids you are missing out! They are so easy to do.
All you need is a plastic water bottle with a lid and an item that you can float in the bottle. This item needs to be filled with some liquid and some air so that the pressure you apply to the bottle can affect its location in the bottle. We used plastic pipettes with a hex nut for weight. You also need a cup to test the pipette to get the right amount of water inside to make it float in the top half of the bottle so when they squeeze it, the diver will dive to the bottom correctly.
My son had to add water to the pipette until we could get it to float in the water at a good height, not too low and not too high. You can test this in a glass of water until you get it right. I like to use colored water in a clear pipette so my kids can see how the water level in the pipette changes as they squeeze the bottle.
You all know how much I love connecting literature to our other subject areas....this lesson was no different. We read a book about a chick who has to be saved by a duckling when he finds out that he can't swim. I challenged my middle son to a more difficult Cartesian diver experiment. We added two divers to a larger bottle. One diver was weighted so that it sank lower in the bottle and the other was lighter. We added a loop to the lower pipette and hooks to the higher one. My son had to use water pressure to lower the hooked pipette down to 'rescue' the other diver and bring it to the top of the bottle. After many attempts he was finally successful.
If you are interested in this lesson plan, you can find it here.
It comes along with reading response worksheets to go along with the books "The Chick and the Duckling" by Mirra Ginsburg and "Duck" by Gail Gibson as well as some scientific worksheets to record their results from their own sink and float experiments.
Happy Experimenting,
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