Salt and Pepper Collector/Selector

Objective

The objective of this experiment is to demonstrate the attractive force between opposite charges.

Materials Required

salt
finely ground pepper
a plastic spoon
a wool cloth

How To Build It

First spread some salt and pepper on a flat surface. Make sure that the salt and pepper are not clumped together. Rub the spoon with the wool cloth in one direction only.

Experiment

  1. Hold the spoon just barely above the salt and pepper. Notice how the salt and pepper fly up to the spoon and cling to it.
  2. Now clean off the spoon and bring it slowly toward the salt and pepper from a distance. At a certain distance (about an inch above the mixture), the pepper will fly up toward the spoon and stick to it, while the salt will remain still.

Trouble Shooting

  1. If the salt and pepper do not appear to be attracted to the spoon, try the following:
    1. Wipe the spoon again with the wool cloth.
    2. Spread the salt and pepper out. Make sure they are not clumping together or stuck to the table.
  2. If, while trying to collect just the pepper you attract the salt also, try the following:
    1. Hold the spoon further away from the mixture.
    2. Separate the salt and pepper more. Make sure they are still mixed, but not clumped or piled on top of each other.
Questions For Thought
  1. Why did the salt and pepper fly up to the spoon?
    ANSWER: We gave the spoon a negative charge when we rubbed the wool across it. This negative charge attracted the salt and pepper and made them cling to the spoon.
  2. Why did the salt remain still while the pepper flew to the spoon when the spoon was held a short distance away?
  3. ANSWER: The pepper is lighter than the salt, and thus the electric charge can overcome the force of gravity more easily.

Additional Information

See: Experiments with Everyday Objects by Kevin Goldstein-Jackson. Prentice-Hall, Inc. 1978. p. 158.


ASU Department of Electrical Engineering
Last Updated: June 21, 2002
Original Page Development by: Matt Dayley and Keith Holbert
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