With this demonstration I ask the students to explain the mechanics of what is going on. Why can I knock the bottom checker out without the rest of them falling over? The explanation is similar to the one for a Coin in a Glass only this time it is the bottom checker moving rather than a card. It might be interesting to note that each time the mass of checkers is different but the effect is still the same regardless of the mass.
Even though the concept is the same for both demonstrations asking the above question gets the students to make the connection in their own minds. If you get them to discuss it with their neighbor then they have to express their understanding in words and they engae in the language of the discipline. Next in pairs get them to draw a diagram of what is going on and they will gain a further depth of understanding. Finally asking the students to present their diagrams to the rest of the class for critical analysis completes the cycle. They have to explain their diagram and the rest of the class have to consider it and analyse it.