To demonstrate the inertia of a stack of discs.
Pile a stack of black draughts discs with one white piece inserted second from the bottom. Then place another disc a foot away on its edge as shown. The press your finger down on the edge of this disc and propel it forward towards the stack. The disc will hit the stack and dislodge the white piece without disturbing the others. This is a demonstration of inertia, because it is the inertia of the black discs that keep them in place while the white disc is knocked out.