Check out these two pictures from the bumper car ride at the fair.
Now look at this picture showing where the roof supports meet the roof.
See that rubber spacer in there? I don't know all the technical details, so I am just making up stuff here. But I assume that is the electrically insulate the top (ceiling) from the floor. I imagine the bumper cars work something like this:
You wouldn't want the cars to have batteries that would need to be recharged and you wouldn't want them to be plug-in type that have cords all over the place. So, they essentially are plug in type cars. One end of the plug is the ceiling and the other end is the floor. That is why they have those poles running on to the ceiling. I imagine there is some type of connector dragging on the floor to complete the circuit.
If you didn't have that rubber spacer between the ceiling and floor, there would be a short circuit.
The thickness of the spacer tells us something about the voltage that the cars run on. How? Well, let me just make the approximation that the two pieces of the support column are like a parallel plate capacitor. In this capacitor, the electric field is essentially constant. In this case, the relationship between the magnitude of the electric field and the change in electric potential is:
Here s is the distance between the plates. Why am I looking at the electric field? Well, if you increase the electric potential between the two plates - or if you get them closer together, the electric field will increase. If the electric field gets too high in air, you get a spark. This is called electric breakdown - for air, this occurs when the electric field exceeds 3 x 10^6 V/m (for DC cases).^
Some Estimates
So, let me estimate the thickness of the spacer. How about 3 cm? That is just a guess. If that were the case, what kind of voltage could you have and get a spark?
There is no way that thing operates at 90kV. What if they built in a safety factor of 100 - meaning the spacer is 100 times thicker than it needs to be? This would put the change in electric potential at 900 Volts. I suspect this is still too high. It is probably 12 volts or something like that.
