Choosing The Right Discus

RIM WEIGHT

Perhaps the most confusing aspect of choosing a discus is understanding the rim weight. Before understanding the rim weight of a discus it is necessary to acknowledge some simple physics related to projectile motion.

So what exactly seperates a 70% discus from one of 90% rim weight?

Inertia.

To allow an easy comparison/discussion we will assume that there is a uniform radius and thickness to both discus’. Due to the heavier rim weight a larger portion of the weight is located upon the outside. Likewise due to the mass being distributed farther from the origin of rotation it will have a greater centripetal acceleration. Because of this angular velocity, the 90% rim weight discus will have greater centripetal acceleration when in full flight and likewise be harder to cause a change in direction.  As per Newton’s 1st Law of Motion. (An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.) The result is that the 70% rim weight discus will be easier to spin than the 90% counterpart.

The question then arises “If you can spin a lower rim weight discus faster and with the same amount of force, why not just throw a low rim weight discus? Won’t it travel further than a high rim weight discus?”

Not quite, we will explain why that doesn’t happen with the concepts of Air Resistance/Gravity and Aerodynamic Lift.

Let’s continue…