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Stone Shifting 2
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Steve Gray
Steve Gray
931 posts

Re: Stone Shifting 2
Aug 27, 2003, 23:55
I could set up a temporary website for pictures, etc. People could email them to me as attachments and I'll upload them. That's probably easier than trying to provide a direct upload capability. I have broadband, so the attachment size is no big deal. If I get a chance to set something up I'll post the details. Let me know if you're still have problems downloading the model, I could email it to you or send you a copy on CD.

When you do get the model try the following: tower height = 5.5m, offset = 1m, leave the other settings at default. I don't know how wide the blocks are (I assumed 1 m). If you increase the width (depth) of the block, it will increase the momentum, so you will have to reduce the offset or height to compensate. I suspect that the original Stonehenge uprights were erected from outside the circle and that the 45 degree slope was to allow the stone to arc into the hole, thus reducing the height requirement of the tower.

If you have already tried some practical experiments, see if the model behaves the same way with those settings. I would appreciate any feedback on this matter. Please bear in mind that the frictional coefficient of 0.8 is merely a guess. I haven't had time to assess it properly. The way to do it is to measure how much force is needed to drag a block of stone over a flat wooden surface. The coefficient is the force divided by the weight of the stone. So if it takes a pull of 7kg to move a 10kg stone the coefficient would be 0.7. You can do it with a spring balance or a string over a pulley with a weight pan on the end.

I have considered how to handle non-uniform blocks in the model. I would need a profile that approximates the block to a collection of small uniform cubes put together rather like a butcher's block. The moment of inertia of the entire block can then be computed as the sum of the moments of each of the small blocks. This can be done in advance of the real-time modelling, so computation time is not critical and hence we can use a very small block size, which will make the approximation quite accurate (how accurate it needs to be, I'm not sure).

My aim is to refine the model until it agrees with ALL our practical tests. Then we can use it to predict the appropriate parameters for the 10 tonner. If that works like a treat, then we can have some confidence that it will work for the 40 ton attempt.
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Re: Stone Shifting 2 (nigelswift)
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