When the directing team “Daniels” came up with the concept for what is easily my favourite video of 2011, I suspect that teaching chemistry wasn’t their first priority. I should know, I even watched the “making of” just to check .. and to geek out at their impressive rig which gave them the ability to shoot it as if it was all done in one continuous shot.

 Still, the idea of walking up the “down” escalator must have been used as a model for teaching the concept of dynamic equilibrium since it was first invented. If the man is walking up the escalator at the same speed as the escalator is descending, even though both he and the escalator are moving – his relative position does not change over time. In equilibria, it is the rate of the forward and backward reactions that are the same.  Even though at the macroscopic level nothing appears to be changing, at the microscopic level there is feverish activity as both forward and backward reactions proceed indefinitely.

As long as you’re in a closed system – and this is where the best bit comes about any model – getting the kids to explain its weaknesses. What behavious can this model explain and what can it not explain? If the man speeds up even a little he will eventually walk off the top of the escalator so this model can’t explain too much about what happens if we make a change to the system.

In Daniels’ video for Battles’ My Machines, a poor chap is doomed to provide us with a different angle on the model as he falls down it for four minutes. There are a few moments where the position of equilibrium is adjusted by external inputs … but we’re already stretching the model to its limits!