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about moment


R is compression force, why it's not 'compressing' the spine ?(ie why it's not pointing towards the spain?)

[ 本帖最後由 qwer 於 2016-1-20 01:09 PM 編輯 ]
   

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how to upload photos?
Thanks

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use imgur

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pic is uploaded, thanks

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引用:
原帖由 qwer 於 2016/1/20 12:04 AM 發表

R is compression force, why it's not 'compressing' the spine ?(ie why it's not pointing towards the spain?)
Actually R is just a reaction of the sum of the other forces. That piece of bone doesn't actively give the force. If the main part of the spine was not in touch of that piece of bone, the R would be zero.

So... you may think the horizontal component of R is to balance that of T. While the vertical component of R is to help that of T, because L + W seems quite large.

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horizontal component of R balances T cos 12 (points to the right).

Take moments about where T acts upon.
clockwise moment by L = (40)(0.24) = 9.6 N m
anti-clockwise moment by W = (520)(0.03) = 15.6 N m

This means that the vertical component of R has to produce a clockwise moment of (15.6 - 9.6) = 6 N m about where T acts upon.  Hence the vertical component of R point upwards.

[ 本帖最後由 abcb_007 於 2016-1-23 03:29 PM 編輯 ]

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thanks , but it's quite difficult to understand

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