Of flying frogs and levitrons

@article{Berry1997OfFF,
  title={Of flying frogs and levitrons},
  author={Michael V. Berry and Andre K. Geim},
  journal={European Journal of Physics},
  year={1997},
  volume={18},
  pages={307-313}
}
Diamagnetic objects are repelled by magnetic fields. If the fields are strong enough, this repulsion can balance gravity, and objects levitated in this way can be held in stable equilibrium, apparently violating Earnshaw's theorem. In fact Earnshaw's theorem does not apply to induced magnetism, and it is possible for the total energy (gravitational+magnetic) to possess a minimum. General stability conditions are derived, and it is shown that stable zones always exist on the axis of a field with… 

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