Stonehenge is going nowhere

In an extension to the Stonehenge problem, consider the mechanical possibilities for an arrangement of frictional rollers.
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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.

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Stonehenge is going nowhere


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?

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Stonehenge is going nowhere