homemade magnetic ball tunnels

The girls were at the science center last Friday. they were very impressed by a set of tunnels that they could make (large tubes with magnets attached on either ends that they could link up in whatever way). I thought it was interesting.

For a long time, i have been meaning to make a water wall. A few factors have detered me from it. Firstly, it has to be made in the bathroom or outside. Putting the water wall in the bathroom means confining playing in it to  bathtime alone. Putting it outside would mean lugging bucket fulls of water outside when the kids want to play in it, and also to sweep the water away after the kids finish playing so that no one will slip on it.

I still havent given up on the idea, but need time to consolidate and come up with a plan.

However, in the meantime, the magnetic ball tunnel boards gave me an excellent idea for the kids to explore how objects move in tunnels. So I worked on it and this is what we came up with.

Everything is attached by magnets to the fridge door, so the kids can move them around. There are holes cut at the bottom of the paper cups, and the little red cup at the bottom is to catch the ball.

Anjali has a good time engineering the balls to flow through the "tunnels", but the problem is that we often dont catch the ball and it rolls under the fridge. I want to sort of get over it by making several small balls out of playdough/ aluminium foil. But the problem with these balls is that they dont roll. The best bet for balls that i have currently is the little plastic easter eggs that Anjali brought back from school. We have some marbles, but I am worried that they will get all over the floor, and also that they are heavy. I tried an avocado seed, but it was too heavy and when it fell, the force of the fall knocked over the little red pot.

Maybe I should do something like the science center and put a longer container at the bottom for the explicit purpose of catching the balls. But what do I use for it??