Do this like you did with the charged rods, carefully rubbing your hands over the sides. The amounts of charge we are moving here are tiny, but the device is very sensitive. The - charge on can 2 is there because charge is conserved and nothing is holding it, and the char ge on the tube is repelling it. Now, suppose you ground the two cans by touching them, then the charge which is not attracted to the tube escapes into your body. This is also the way you put a charge opposite to that on the tube on a single sphere .
Geometry here means that the conductors are of a different size and shape.
I would have grounded it. I rub the cutting board with the oven bag. I found that the oven bag which I used to charge the cutting board repels the oven bag I used to charge the golf tube, so the cutting board and the golf tube must be charged the same. I put the pie pan on the charged plastic and grounded it with my finger. I felt a spark when I grounded it.