In the Stonehenge problem a block of stone is moved by rolling along the top of a layer of logs. In this problem the block of stone moves twice as fast as the logs. A student suggested that maybe using 2 layers of logs would make the stone move even faster relative to the ground.
The student modelled the arrangement in the free software program Phun, modelling the logs as cogs to prevent slipping. She was surprised by the outcome -- can you work out what will happen? What will happen if the friction between various surfaces is reduced? Do any questions arise for you?