Posted by Jock on May 05, 2006 at 10:41:28 from 81.76.86.2 user Jock.
In Reply to: Re: Boxpoc wheels (was Valve Gear was Thorpe Station... ) posted by John Nichols on May 05, 2006 at 02:00:43:
So holes help inertia, which is why we don't like solid wheels.
No, no. Holes reduce inertia. Though inertia can cause holes as in SD. Also inertia stops politicians and civil servants from ever admiting their mistakes which causes lots more holes.
I=mr2 is the formula for the moment of inertia of a single particle, the moment of inertia that keeps the wheels rotating smoothly is given by formula for a thin disk I=1/4mr2. However, the formula for calculating the damage done to track is proportional to the axle weight rather than moment of inertia. I remember reading somewhere that it's proportional to the 5th power of the axle weight. Which apart from the obvious environmental benefits gives us an excellent economic incentive to put heavy long-distance freight onto rail rather than road.