For a classroom demonstration,
it should be straightforward to build a simple vertical
channel that is sturdy enough to withstand the impact of
the ball as it bounces between the two surfaces. For a quick
and dirty demonstration, I have found that a cinder block
standing on end next to a wall works well. The cinder block
is useful because it can be easily moved toward or away
from the wall to adjust the channel width, while the block’s
weight helps it to resist the force of the superball bouncing
between the block and the wall. Similarly, two desktops facing
one another could be used or one table top and a thick
piece of wood