Perception of the Moment of Inertia of Hand Tools

Abstract

Suppose I ask you to select one from five identically manufactured baseball bats. Apart from surface texture and color, the dimensions and mass of the bats are exactly the same. However, as you test out the bats with a few swings you would very likely arrive at a definite preference for one or the other of the five. The mass distribution within the wood of the bat changes its feel. In mathematical terms, this difference in feel is best described by the moment of inertia.

This presentation demonstrates the relationship between the measured moment of inertia of a hand implement and the users perception of the stimulus. Simple mock tools, all with the same weight and size but varying moments of inertia were rated against a standard according to the amount of moment of inertia. A functional relationship between the perception and the magnitude of the stimulus has been established.

Observers of this presentation will be able to familiarize themselves with sensations and numerical values of moment of inertia of various hand tools and experimental test pieces. The measurement of moment of inertia is complicated by the geometry of the tool, the weight distribution, and the point of hand grasp. The values are unfamiliar. The concept of what causes the sensation is not simple and, as others have pointed out, our vocabularies are usually inadequate to describe what causes the change in sensation that is felt with a change in moment of inertia.