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Grade 3 through Grade 5 (Elementary School)
Overview and Purpose:
This experiment is a childhood favorite. Mixing cornstarch and water together creates a substance that seems to be both a solid and a liquid. Students enjoy rolling it into a ball and then watching it run through their fingers when they stop.
The student will be able to
*explain why cornstarch and water is called a suspension.
*apply different amounts of pressure to a mixture of cornstarch and water and describe the results.
Review with students the definitions of liquids and solids. Tell the students that they are going to work with cornstarch and water today to decide if it is a liquid, a solid, or neither.
Divide the students into pairs and give each group one cup of cornstarch, one cup of water, a bowl, a spoon, a fork and a block. Have the students pour the cornstarch into the bowl and then add some of the water while stirring with the fork. They should add enough water that the mixture is thick and gooey.
Have the students complete the worksheet as they manipulate the mixture in different ways. They can press on it, try to pick it up with a spoon, push the block down on it, and set the block on it.
After they have had time to experiment with the mixture, come back together and discuss the results. Tell them that the mixture is called a suspension. It acts like a solid when pressure is applied because the molecules bind together, but when there is no pressure it acts like a liquid because the molecules separate.
Sample questions for a class worksheet:
1. Do you think this mixture will be a liquid, a solid, or neither? Why?
2. Press on the mixture with the palm of your hand. What happens?
3. Try to push the block to the bottom of the pan. What happens?
4. Set the block on top of the mixture. What happens?
5. Why do you think there were two different results?
This mixture is so much fun to play with. Students will not want to stop playing and come back for discussion. Depending on your tolerance for a mess you could fill a child's swimming pool with an inch or two of the mixture and have students walk on it in their bare feet or roll balls of various weights across it.