I dont understand homopolar motors

[pkc111]

I understand the diagram above where the blue stuff might be mercury like in Faraday's mercury motor. I don't understand why the liquid moves but... it is a conductor so why doesn't the current (moving electrons) feel the force and leave the liquid stationary?
Similarly in this motor its the liquid that moves?

Many Thanks

 

[David Lewis]

There are homopolar motors that exert a force on the electrons in the (solid) rotor, and the electrons then carry the atomic nuclei with them, for example in an electrostatic voltmeter.

However in this case I believe the cell exerts an electrostatic force on the electrons in the copper wires and in the liquid, and the moving electrons create a magnetic field. What we are seeing is the interaction between the permanent field magnet and the magnetic field created by the current.