All cooks have been there: you're following a recipe and accidentally mix the ingredients too soon. What if you could turn back the clock and pick the mixture apart bit by bit? Impossible, right? Think again! Experiment with the process of induction and the principle that "opposites attract" by separating salt from pepper using nothing more than a plastic spoon.
This experiment depends on building an electrical flow by rubbing plastic against wool. As the negatively charged plastic spoon is lowered, it charges the salt and pepper through a process called induction. The nearest surface of the salt and pepper gains a positive charge and the far side a negative charge. As the spoon is slowly lowered, the grains of pepper will jump toward the spoon first. You need to see it to believe it!
What You Need:
- 1 teaspoon table salt
- 1 teaspoon ground black pepper
- Plastic spoon
- Wool sock (your hair will do if there’s no sock handy)
- Piece of paper (optional)
What You Do:
- Have your child mix the salt and pepper on a smooth, dry surface like the table.
- Encourage him to rub the spoon vigorously against the wool sock (or his hair).
- Instruct your child to slowly and very carefully lower the spoon toward the salt and pepper mixture.
- When it’s an inch or two from the surface, pause and watch as the pepper jumps up, grain by grain, to the spoon’s surface.
- Stop the experiment here if you simply want to show how it works. To complete the separation, continue with steps six and seven.
- Slide a piece of paper under the spoon and shake the pepper grains onto it.
- Rub the spoon against the sock again and repeat until all the pepper has “jumped” to the spoon and only salt remains.
The pepper jumps up first because it’s lighter than the salt. That’s why lowering the spoon slowly is so important: move too fast and the salt and pepper will jump up together. If you want to complete the “tidying up” after all the pepper has been removed, simply carry on with the process, moving the spoon a bit lower.
By Sean Connolly
Adapted with permission from "The Book of Totally Irresponsible Science." Copyright 2008 by Sean Connolly. Used with permission of Workman Publishing Company, Inc., New York. All Rights Reserved.
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