In a message dated 12/11/2007, tchannel1@............ writes:

Hi Folks,   Just wondering about  materials for roller on roller or balls on 
plates.   I know the  limitations of glass, but a question about its 
smoothness, is the surface of  glass as smooth or smoother than these hardened and 
polished  steels?

Hi Ted,
 
    Probably about the same. You get an optical finish  with fine polish on 
metal. However glass is a rapidly solidified liquid.

My second question is one of friction: If you  have one ball on one plate you 
would have one point of friction.  If you  have one ball resting between two 
rollers, (in the V) you would have  two points of friction, but the load would 
be divided, because its resting on  two points, so is the end result of 
friction loss the  same?


    It is the surface to surface properties which are  important. The actual 
static friction is proportional to the load, so  halving it and using two 
points will likely give a very similar result. However,  if you put a fixed 
vertical load on a ball resting on two rods, the loads  at the two points are 
increased to give the same resolved vertical  force.  
 
    When we talk about friction in pendulum  suspensions, it is not this 
static friction to which we are referring. It is the  tiny rolling contact loss as 
the materials are compressed and relaxed. No  materials are perfectly 
elastic. Glass is poor in this respect and tends to chip  easily.
 
    Regards,
 
    Chris



   





In a message dated 12/11/2007, tchannel1@............ writes:
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Hi Folks,   Just wondering abou=
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  materials for roller on roller or balls on plates.   I know the=20
  limitations of glass, but a question about its smoothness, is the surface=20=
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  glass as smooth or smoother than these hardened and polished=20
  steels?
Hi Ted,
 
    Probably about the same. You get an optical fin=
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with fine polish on metal. However glass is a rapidly solidified liquid.
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My second question is one of friction: If=
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  have one ball on one plate you would have one point of friction.  If=20=
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  have one ball resting between two rollers, (in the V) you would=20=
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  two points of friction, but the load would be divided, because its resting=
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  two points, so is the end result of friction loss the=20
  same?

    It is the surface to surface properties which a=
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important. The actual static friction is proportional to the load, so=20
halving it and using two points will likely give a very similar result. Howe=
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if you put a fixed vertical load on a ball resting on two rods, the loa=
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at the two points are increased to give the same resolved vertical=20
force.  
 
    When we talk about friction in pendulum=20
suspensions, it is not this static friction to which we are referring. It is=
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tiny rolling contact loss as the materials are compressed and relaxed. No=20
materials are perfectly elastic. Glass is poor in this respect and tends to=20=
chip=20
easily.
 
    Regards,
 
    Chris