Download 20-020 Science First Instructions for Barlow`s Wheel Parts

2010 Science First®
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20-020 Science First Instructions for Barlow’s Wheel
Parts List:
057112
24-20020
Barlow’s Wheel
Instructions
Introduction: The Barlow’s Wheel was designed by Peter Barlow, an English
mathematician, in 1822. Barlow’s Wheel was considered to be one of the first electric
motors supplied by continuous current. While it does work, the design is considered too
inefficient to do useful work. The device is able to function via the use of eddy currents.
What is an Eddy Current? It is a well known fact that subjecting a conductive material to
an electric field will set up a current in that material. What is less well known is that it is
possible to localize a current and prevent it from flowing. A useful analogy is a river:
picture a river as an electric current, flowing along. At certain irregular points along the
river bank, the water may become trapped, and swirl around helplessly while the rest of
the river flows onwards.
Eddy Currents function the same way. If you can induce a current in a portion of a
conductor that is physically isolated from the rest of the material, an Eddy Current may
be formed. Eventually the current will dissipate, but in the short term they can prove to be
quite useful.
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Science First®, 86475 GENE LASSERRE BLVD. YULEE, FL 32097, U.S.A.
904-225-5558·FAX 904-225-2228·[email protected]· www.sciencefirst.com
2010 Science First®
______________________________________________________________________________________
For classroom purposes, electricity and magnetism are the same force. This means that an
electrical field, such as an Eddy Current, is magnetic. Thus, if we can induce eddy
currents, we can attract them with a powerful magnet.
Operation: To use your Barlow’s Wheel, first install 4 AA batteries. The twin battery
holders are connected in parallel. Due to the inherent inefficiencies of this design, the
double current supplied by parallel batteries is essential. In addition, the wheel rotates on
Teflon cone bearings, providing a very low friction environment. This lower friction
helps make up for the lower efficiency.
Next, adjust the brushes. They need to just barely touch the spokes of the wheel, without
getting caught between them. These brushes will allow electricity to flow from the
batteries into the wheel.
When you have set up the unit, flick the switch either left or right, and give the wheel a
gentle push. It should start spinning on it’s own, continuing as long as there is a supply of
current.
How does it work? Notice that the brush is only large enough to touch one spoke at a
time. When it does, an electric current gets induced in the brass spoke. Since the spoke is
isolated from its neighbors by air, an insulator, the current temporarily has nowhere to go.
It becomes an Eddy Current.
We learned above that Eddy Currents produce magnetic fields. Mounted on the gimbal of
Barlow’s Wheel are 4 very powerful neodymium magnets. The magnetic field produced
by these is strong enough to attract the Eddy Current in the end of the spoke, which gives
the wheel a tiny torque. This is enough force to advance the next spoke against the brush,
where it will be energized and repeat the process.
As long as the supply of current remains constant, the wheel will spin. Please note that
the Eddy Currents do not remain forever; that particular phenomenon is only present in
super conductors. Eventually, the electricity will find its way into the center of the disc,
through one of the spokes, and out the brush on the other side. This process takes place
far too quickly to notice. However, it is delayed just enough that the eddy current is
drawn into the magnetic field.
Warranty and Parts:
We replace all defective or missing parts free of charge. Additional replacements parts
may be order toll-free. We accept Visa, MasterCard, American Express and Discover as
Well as School P.O.s. All products warranted to be free from defect for 90 days. Does
not apply to accident, misuse or normal wear and tear. Intended for children 13 years of
age and up. This is not a toy. It may contain small parts that can be a choking hazard.
Adult supervision is required. Designed and prototyped in the U.S.A. Made in China
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Science First®, 86475 GENE LASSERRE BLVD. YULEE, FL 32097, U.S.A.
904-225-5558·FAX 904-225-2228·[email protected]· www.sciencefirst.com