Two-Liter Bottle Levitation
John C. Lahr 8/11/2004

 

This design was developed while attending the Teacher Institute at the Exploratorium in August 2004.

Required Parts:

bullet One small Neodymium-Iron-Boron (NeFeB) magnet, such as a cubic magnet with dimensions of 3/32-inch on each side ($0.15 from Wondermagnets, #0049)

or a disk-shaped magnet with dimensions of  1/8-inch diameter by 1/16-inch thick (also $0.15 from Wondermagnets #0048).
(http://www.wondermagnets.com/)



bulletTwo ceramic donut magnets with dimensions of about 1-cm thick, 5.3-cm diameter, with 2-cm diameter central hole.
bulletOne 9-inch length of 10-32 threaded rod
bulletOne 10-32 wing nut
bulletGraphite, either:
bulletOne carbon planchet (Graphite Planchet, 25.4-mm diameter) ($8 for ten from Ted Pella; http://www.tedpella.com/carbon_html/16524.htm ) or
bulletOne piece of pyrolytic graphite, 32-mm by 16-mm ($6 for a package of 3 from Science Toys; http://www.scitoys.com/ )
bulletOne CD (which will never be used again as a CD!)
bulletOne 2-liter plastic bottle with cap
bulletCork from bottle
bulletPlaster, such as "Fix-it all" patching compound.
bulletHot glue
bulletSand paper

Construction:

bulletDrill a 3/16-inch hole in the center of a cork.
bulletSand the cork, if necessary, so that it will seat tightly inside the ceramic donut magnets.
bulletPush the cork into the center of the donut magnets, press the end of the threaded rod into the cork and then adjust the orientation of the magnets so that they do not wobble when the rod it rotated slowly.  Then apply hot glue to the junction of the magnets with the cork and the cork with the rod.
bulletTo remove the label from the 2-liter bottle:
a) make a vertical slit through the label
b) fill the bottle with very hot but not boiling water
c) slowly peal the label from the bottle
d) vigorously rub any areas with glue residue with a dab of peanut butter
e) clean off the peanut butter with warm soapy water
bulletCut the bottom 6-cm off of the 2-liter bottle.  Be careful, as this can be hazardous.  I used a band saw, but a box cutter could also be used.
bulletMake five vertical slits in the bottom piece so that it will be able to slide up into the top of the bottle.  Each slit will be about 2-cm long.


bulletDrill a 7/32-inch hole down through the center of the bottle cap.  This hold needs to be large enough for the rod to slide through with no resistance.
bulletSlide the rod up through the bottle and its cap and screw on the wing nut.
bulletInvert the cut-off bottom of the bottle and press the upper portion down over it, creating a space about 6-cm high.
bulletGlue the graphite to the center of the CD.  Use hot glue within the hold below the graphite, but be careful that the CD will still rest flat on a table.  If the glue sticks down too far, cut off the excess with a razor blade.
bulletMix a small quantity of plaster and use it to create a smooth ramp between the top of the CD and the upper surface of the graphite.
bulletWhen the plaster is dry and hard, smooth any bumps with steel wool or fine sand paper.
bulletPlace the small NeFeB magnet on the CD and cover it with the bottle.


Operation:

By carefully adjusting the wind nut, the NeFeB magnet can be made to levitate above the graphite.  If too much of the rod hangs in the bottle, the magnet will jump up and stick to the bottom of the bottle.  In this case, lift the rod up until the cubic magnet falls down again, then adjust the wind nut and lower the rod again.  If too little of the rod hangs in the bottle, the magnet will lie on the planchet and will not levitate.

Levitation will be clearly achieved when the cubic magnet moves around freely just a fraction of a millimeter above the planchet.


View from above.

 


View of Base

 
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