# Stonehenge is going nowhere

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

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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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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Think about the directions the logs are trying to go

Like Stonehenge 1, this is an exercise in having a feel for
mechanics.

One way to think about this one is that when you push the stone from left to right, the top layer of logs wants to move clockwise, and from left to right. The bottom layer of logs then wants to move anti-clockwise, and from right to left. However the bottom layer cannot move left since the logs on the top layer are going right.

One way to think about this one is that when you push the stone from left to right, the top layer of logs wants to move clockwise, and from left to right. The bottom layer of logs then wants to move anti-clockwise, and from right to left. However the bottom layer cannot move left since the logs on the top layer are going right.