Actually, neither the coefficient of friction nor the friction force
does change. See my next message to Michael Pardee.
If I understand what they are saying, the smaller radius results in less
rotational friction, which would be a linear relationship with respect to
parasitic torque. That is, if the original torque was 50% on the threads and
50% on the bolt head, cutting the radius in half would cause only 25% of the
torque to be used to overcome bolt head friction and would put the remaining
75% of the torque on the threads.
Note that this is not the area but the radius that is changed. In theory,
friction is independent of area. What they seem to be describing is
'Frictional Force' is calculated by multiplying the coefficient of friction
times the normal force. Normal force is the perpendicular force in a system.
It can be quite difficult to determine the correct coefficient of friction
to utilize when there is plating involved, two different types of materials,
This same problem is why some of these highway patrolmen's estimates of a
car's speed that was involved in an accident can be total b.s. Many factors
such as road film, tire condition, loose gravel and brake conditions should
be taken into account, technically, and there's simply no way that this
could be calculated accurately at the scene of an accident.
Got it. It is the integral of the travel. That is, friction at the bolt
head (washer) is proportional to,
friction = D(l)^2/2 - D(s)^2/2
D(s) = small diameter
D(l) = large diameter
Note that D(l) is the smaller of bolt head diameter or large diameter
of the washer.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.