I just learned something: an electric dipole in a capacitor

[BrianHG]

I did not expect the second result after the conductor was removed:

[SpiralElektronik]

The conductor provided a channel so that the charge distribution between the poles could change. With no conductor between the poles theres no way for the field to redistribute the charge. When the conductor is removed the charge stays just as static electricity will stay on a balloon. No magic here but a cool demonstration of electric fields non the less!

[Marco]

Question is why the unchargd metal barbell with insulated rod (presumably) is mechanically stable. Guess the spherical shapes and the near perfect centering makes the capacitance of the system almost perfectly constant regardless of rotation.

[BrianHG]

I have another question:
Does the length, shape, and bend of the aluminum foil effect the results?
Could it have been longer to the edge of the 2 spheres?
Could it have been narrow like a flat wire?
What if it were shorter, just the length in between the 2 spheres?

[RoGeorge]

When you put a piece of wire (here the Al foil) inside a capacitor, you get two series capacitors.  When voltage is applied, the 4 plates of the two series capacitors will charge with +/-/+/-.

This means at one end of the Al foil we have -, the other end +.  Some of the charges will stick to the plastic balls after the foil is removed, each ball will get opposing polarity charges, which will turn them into a polarized dipole.  Once the charges stick, when an electric field applies, the polarized dipole will orient itself into the E field.

Could have been used any other way to deposit some electric charges, e.g. the triboelectric effect, and the plastic dipole will orient itself just the same.  https://youtu.be/2GQTfpDE9DQ

Static electricity can be very fun:

[CatalinaWOW]

Electric field strength is greatly increased by addition of foil strip.  Before the conductor is added field strength is 5000V divided by plate separation, by eyeball something on the order of 500 V/cm.  Since there is no voltage across the conductor when it is added, the field strength is the same 5000V, but divided by the total spacing between the conductive elements which is something like 10 times shorter.  Charges which stayed put originally got ripped from their home atoms and moved. 

A variation on the same experiment that would be interesting and informative would be to modify the foil strip so it covered the ends of the balls.  Field strength would be essentially the same, but the balls would be totally isolated from it, and I would expect no retained charge.