Doughless
I see the chart claiming that "rolling resistance" decreasing as the car moves has to do with inertia, and not what I would call friction on the bearings or "rolling resistance" lessening.
the chart doesnt' show the resistance of a stationary car (0 mph). i don't believe it's the same as at 5 mph
i don't think "inertia" is the reason dynamic friction is < static friction. inertia is the principle that things at rest remain at rest and things in motion, remain in motion, quantified in Newtons equation:
acceleration = mass / force = mass / (tractive effort - resitance)
this equation doesn't describe the speed, just the change in speed, acceleration
i don't understand why the loaded resitance is < the empy resistance. my guess is the coefficient of friction is actually affected by the pressure on the bearings. no doubt it's more complex.
and if the guy (?) who allocate motive power for a train needs to know how much resitance there is, he's interested in that value at speed, hence the charts
Doughless
Things like aerodynamics, gravitational pull on grades, intertia, all impact how "easily something rolls" but that's not the samething as rolling resistance, at least how I think of it.
the resistance chart captures two values, others include gravity on grades and braking
Doughless
It corroberates my thought that adding weight to a car will keep it staying put as the loco couples up to it because there is more friction on the bearings. Not to mention the greater the inertia
if the resistance is about the same regardless of weight, then it's the inertia, the added mass that requires more force to accelerate the car away from the loco when coupling
some of these concepts are not obvious. nase spent lots fo $$$ to show that a feather and hammer fall at the same speed on the moon without the drag of air resistance