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I am interested in your use of the term "mechanism". To what does
that
refer, and what insight does that give us in solving the problem.
For the hoop rolling down the incline (which is close to
where this thread started) there is a transfer of energy
from the gravitational potential energy of the system of
hoop and earth to translational and rotational kinetic
energy of the hoop. The mechanisms are the gravitational
force between the hoop and the earth and the contact force
between the incline surface and the hoop.
The contact force is a constraint force. It doesn't do any
work but, together with the gravitational force, it
determines the motion. First it stops the hoop from
falling. Second it supplies the torque that leads to the
rotation. That's why I refer to it as (part of) the
mechanism for the process to occur. The process gives us
the motion we observe and then, acting like accountants, we
can do our sums to finds how much energy is in each of the
different forms.
I interpret your reference to the contact force as meaning the
force
normal to the surface of contact. Since that force is through the
center
of rotation, it cannot be responsible for the torque that produces
the
rotation.