Constructing and Studying a Levitating Frictionless Bearing

1
Constructing and Studying a Levitating
Frictionless Bearing

• Ruth Toner
• Senior Project Speech
• 6-10-03

2
Superconductors The Basics

• First discovered 1911 by Heike Kamerlingh Onnes.
• Above critical temperature, superconductor
  behaves like normal material, with high
  resistivity
• - Below Tc, has zero resistance
• - If current is established in loop of
  superconducting material, will continue
  indefinitely.
• - Other conditions superconductor only works
  when current density and magnetic field are below
  critical values Jc and Hc.

Background www.superconductors.org
3
Type I Superconductors -- The Meissner Effect

• Zero resistivity of superconductor means that
  material can act as perfect dimagnet
• When superconductor is exposed to magnetic flux,
  field induces current on surface
• Induced current creates opposing magnetic field
  which leads to force of repulsion between magnet
  and superconductor
• In case of Type I superconductor, magnetic field
  is completely expelled from superconductor
• - force strong enough to cause levitation

http//hyperphysics.phy-astr.gsu.edu/hbase/solids/
meis.html
http//www.imagesco.com/articles/supercond/06.html

4
Type II Superconductors Flux Pinning
-Type II Superconductor contains small
impurities which allows some magnetic flux to
pass through filaments in the material -flux
lines become pinned in place any attempt to
move the superconductor up or down will create a
restoring force -combination of Meissner Effect
repulsive force and flux pinning restorative
force causes levitation

• Advantages
• Higher critical temperatures
• horizontal position of superconductor also fixed

http//hyperphysics.phy-astr.gsu.edu/hbase/solids/
meis.html
5
Materials
6
Creating the Mount
AutoCAD Drawing
CAD drawing
Materials base aluminum handle G10
7
A Levitating Frictionless Bearing Photos
Before The magnet rests on supports
on top of the superconductor, not levitating.
During cooling The mount is lowered
into liquid nitrogen and allowed to cool to 77K,
under YBCOs critical temperature. The YBCO
becomes superconductive.
8
A Levitating Frictionless Bearing Photos
The mount is removed from the liquid nitrogen,
and the supports are knocked out. The magnet
floats in midair, and can only be moved by
applying strong pressure.
9
Studying the Bearing Part 1 Finding the
Spring Constant and Resonant Frequency

• The restoring force F applied by objects like the
  bearing can be described by Hookes law F-kx,
  where k is some constant
• The frequency of vibration f is described by
• Increments of weight were placed on the magnet at
  three different initial heights, and the
  resulting displacement was measured these data
  points were graphed, and the regression line
  slope was used to calculate constant k, and then
  frequency f

At 4 mm k1.7547 f16.88 s-1 At 9
mm k1.0761 f13.22 s-1 At 16
mm k.8057 f11.44 s-1
10
Studying the Bearing Part 2 Finding the Spin
Down Time Constant
-Because the bearing doesnt make surface contact
with anything, it is presumed nearly
frictionless -Some drag forces do exist, however
(e.g., air drag), so that the rotational
frequency f behaves according to
, where t is the time constant for rotational
decay, the time it takes for f to decrease by
63. -The time constant was calculated by
monitoring the number of rotations in a 10 second
period every minute a regression time was
plotted to achieve a value for t. This was
tested at four separate heights.
Example rotational frequency decay at 12.70 mm