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Whelmer #31: Static Charged 2x4s
 Description:
A small static charge is used to attract and move a large piece of lumber.
Science process skills:
- observation
- prediction
Complex reasoning strategies:
- deduction
Standards:
K-4:
- Use data to construct a reasonable explanation (Standard A.1.4).
5-8:
- Energy is a property of many substances and is associated with electricity.
Energy is transferred in many ways (Standard B.3.1).
9-12:
- The electric force is a universal force that exists between any two
charged objects. Opposite charges attract while like charges repel.
The strength of the force is proportional to the charges and, as with
gravitation, inversely proportional to the square of the distance between
them (Standard B.4.3).
Above Standards from the National
Science Education Standards.
Content topics:
- static electricity
- friction
- attraction
- repulsion
You will need:
- long piece of lumber; an 8' 1x4, 2x4, or 4x4 works well
- watch glass, soup ladle, or ice cream scoop
- lubricating oil
- balloon
- piece of wool cloth or fur
Instructions:
Invert the watch glass, soup ladle, or ice cream scoop on a table top. The
smooth convex surface is used as a pivot for the lumber. Place a few drops
of oil on top of the curved surface. Carefully balance the board on the
pivot. The oil allows the board to rotate freely.
Place a static charge on the surface of a balloon by rubbing it in one direction
on a piece of wool or fur. Hold the charged balloon a few inches from one
end of the balanced board. The board moves towards the balloon.
Presentation:
Most students are familiar with the standard static electricity demonstrations
of picking up bits of paper with a charged comb, or "sticking"
a charged balloon to the wall. This is a dramatic extension to those activities.
Allow students to demonstrate the effect of static charges on small bits
of paper or their hair. Ask them what conclusions they can make about static
electricity. (Some might suggest that it is a weak force.)
Use a charged balloon to attract some small bits of paper. Ask students
what effect they think the charge that picked up the paper would have on
a large piece of lumber. (Some might suggest that it would have little or
no effect.)
Balance the board on the lubricated pivot. Recharge the balloon with the
same number of strokes you used when picking up the bits of paper. Hold
the balloon near the board. It rotates.
Content:
The action of stroking the balloon with a piece of cloth causes some electrons
to be dislodged from the cloth and deposited on the balloon. If you hold
the charged balloon near the cloth you may be able to hear the snap of miniature
lightning bolts as the electrons jump back to the cloth.
The rule that most students remember about static charges is "like
charges repel and unlike charges attract."
The electrons on the surface of the charged balloon give the balloon a negative
charge. When the balloon is held near the board, the charge on the balloon
affects the position of the electrons in the board creating the opposite
charge on the surface of the board. This process is called induction. The
charge difference between the balloon and the board is sufficient to cause
the attraction.
Assessment:
Type: small group or individual.
Content/Process: static electricity, induction.
Age/Level: intermediate and higher.
Research and investigate lightning in a text or other resource material
or through oral interviews with weather professionals. Describe through
an oral or written report how the movement of the board by the balloon is
similar to and different from the production of a lightning bolt. Students
should be assessed on their understanding of induction and electrical discharge.
Notes:
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