This problem has deliberately been left open-ended, but if children have explored the interactivity in the Turning Cogs
problem, then they will become familiar with the way that cogs work. Allowing them to experiment and talk about their discoveries with each other might be the best way to get them going on this
If the interactivity is not available,you may like to print off this sheet of cogs
to cut out and give to the children, or use on an OHP.