Salt and Pepper Collector/Selector
The objective of this experiment is to demonstrate the attractive force
between opposite charges.
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.
- 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.
- 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.
Questions For Thought
- If the salt and pepper do not appear to be attracted to the spoon,
try the following:
- Wipe the spoon again with the wool cloth.
- Spread the salt and pepper out. Make sure they are not clumping
together or stuck to the table.
- If, while trying to collect just the pepper you attract the salt also,
try the following:
- Hold the spoon further away from the mixture.
- Separate the salt and pepper more. Make sure they are still mixed,
but not clumped or piled on top of each other.
- 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.
- Why did the salt remain still while the pepper flew to the spoon when
the spoon was held a short distance away?
- ANSWER: The pepper is lighter than the salt, and thus the electric
charge can overcome the force of gravity more easily.
See: Experiments with Everyday Objects by Kevin Goldstein-Jackson.
Prentice-Hall, Inc. 1978. p. 158.
Last Updated: June 21, 2002
Original Page Development by: Matt Dayley and Keith Holbert
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