This applet is a simulation of an experiment in which
an aluminum sphere sitting on the bottom plate of a
capacitor is lifted to the top plate by the electrostatic
attraction generated as the capacitor is charged. While
the sphere is in contact with the lower plate, their
surface charge densities are approximately equal. Thus,
as the capacitor is charged, the charge density on the
sphere increases proportional to the potential difference
between the plates. In addition, energy flows into the
region between the plates as the electric field builds
up. This can be seen in the motion of the electric field
lines as they move from the edge to the center of the
As the potential difference between the plates increases,
the sphere feels an increasing attraction towards the
top plate, indicated by the increasing tension in the
field as more field lines "attach" to it.
Eventually this tension is enough to overcome the downward
force of gravity, and the sphere is "levitated".
Once separated from the lower plate, the sphere's charge
density no longer increases, and it feels both an attractive
force towards the upper plate and a repulsive force
from the lower one. The result is a net force upwards.
In this simulation we have placed a non-conducting
barrier just below the upper plate to prevent the sphere
from touching it and discharging.