On 10 Mar 2008 at 0:05, Fred lunnon wrote:
Incidentally, can we assume that the (interior) of the ball is entirely rigid?
Yes -- things aren't allowed to slide around inside or anything interesting like that.
If so, it does seem difficult to imagine how some of the configurations on offer can be justified by dynamical considerations alone! WFL
Yup, that's what I've been thinking. But month after month they come out with more "core designs". The two big things they talk about are "radius of gyration" and the "RG differential". I'd think that even if those are the key "dynamic criteria" that determine how a ball reacts, it'd be easier to get a particular set of values with some sensible-seeming mass-distribution, rather than these mushrooms, stacks, wedding cakes, etc... Another interesting thing behind the core shape is the idea of "track flare". What happens is that the ball is drilled so that when the bowler throws it the rotation-axis is NOT aligned with the weight-axis. This means, of course, that the ball "wobbles" as it rolls until it settles down to a true roll [with the weight-axis aligned with the rotational axis]. What's happening is that the surface of the bowling ball is, basically, sandpaper but sandpaper that "clogs" very easily [in this case, it clogs with the oil/dressing on the lane]. If the ball rolls consistently, after a rotation or two the ball-surface contacting the lane will be all oiled-up and the friction will go WAY down [and the ball will basically just-skid and not hook]. BUT: with the "Wobble", with each revolution, as the ball precesses, *new*surface* keeps coming into contact with the lane and so there's lots of friction [and so lots of 'grab'] for a long way]. That wobble is called "track flare". /Bernie\ -- Bernie Cosell Fantasy Farm Fibers mailto:bernie@fantasyfarm.com Pearisburg, VA --> Too many people, too few sheep <--