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Re: [Phys-l] ? passive force of constraint



The usual definition of contact is that two objects are in contact if
they exert nonzero contact forces on each other. According to this
definition, if there isn't a contact force, then the two objects aren't
in contact.

I prefer to define a single interaction between two objects in contact.
This single interaction can be resolved into a normal component and a
friction component. At the microscopic level, there are a large number
of interactions between the charged fundamental particles in the two
objects. The sum of all these forces is the contact force. Resolving
each of the electromagnetic forces between each pair of charged
fundamental particles before summing doesn't make sense to me. I prefer
to sum first, get an overall contact force, and then resolve it into two
components, one of which is normal to the surface of contact, and the
other of which is tangential to the surface of contact. I don't perform
these sums ab initio, of course, but conceptually, it makes more sense
to me to define a single overall contact force before resolving it into
components.

Daniel Crowe
Loudoun Academy of Science
dan.crowe@loudoun.k12.va.us
rmcder@gmail.com 07/20/07 12:24 PM >>>
Where there is contact, there MAY be an interaction/force. To be safe,
one starts out with the expectation that there is a force acting, but
that may not be the case. Additionally, a surface is typically capable
of TWO intereactions; normal and frictional.