Manitunc, You wrote, "To use your truck/sports car analogy however, a truck would be less likely to be knocked off its straight path than a sports car hitting the same bump. I dont know that the analogy works because the tonearm is not moving, and therefore has no momentum inertia of its own, only its fixed inertia as an impediment to motion."
I don't really see what you are getting at. The tonearm most certainly does move, in the lateral plane it has to move in order for the stylus to trace the groove, in the vertical plane we don't want it to move (up and down), but it will to a degree that is directly dependent upon the compliance of the cartridge (the springiness of the cantilever) and the mass of the whole ensemble of the tonearm/cartridge. Obviously, the less vertical motion of the tonearm wand, the better.
As an aside, "momentum" and "moment of inertia" are two different things. Don't know what "momentum inertia" is. Finally, for both a truck and a sports car, the correct shock absorber damping will result in the least reaction to a "bump". (I don't really like my own sports car/truck analogy so much, either.)
I don't really see what you are getting at. The tonearm most certainly does move, in the lateral plane it has to move in order for the stylus to trace the groove, in the vertical plane we don't want it to move (up and down), but it will to a degree that is directly dependent upon the compliance of the cartridge (the springiness of the cantilever) and the mass of the whole ensemble of the tonearm/cartridge. Obviously, the less vertical motion of the tonearm wand, the better.
As an aside, "momentum" and "moment of inertia" are two different things. Don't know what "momentum inertia" is. Finally, for both a truck and a sports car, the correct shock absorber damping will result in the least reaction to a "bump". (I don't really like my own sports car/truck analogy so much, either.)